********************* GNU Parallel Tutorial ********************* This tutorial shows off much of GNU \ **parallel**\ 's functionality. The tutorial is meant to learn the options in and syntax of GNU \ **parallel**\ . The tutorial is \ **not**\ to show realistic examples from the real world. Reader's guide ============== If you prefer reading a book buy \ **GNU Parallel 2018**\ at https://www.lulu.com/shop/ole-tange/gnu-parallel-2018/paperback/product-23558902.html or download it at: https://doi.org/10.5281/zenodo.1146014 Otherwise start by watching the intro videos for a quick introduction: https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1 Then browse through the examples (\ **man parallel_examples**\ ). That will give you an idea of what GNU \ **parallel**\ is capable of. If you want to dive even deeper: spend a couple of hours walking through the tutorial (\ **man parallel_tutorial**\ ). Your command line will love you for it. Finally you may want to look at the rest of the manual (\ **man parallel**\ ) if you have special needs not already covered. If you want to know the design decisions behind GNU \ **parallel**\ , try: \ **man parallel_design**\ . This is also a good intro if you intend to change GNU \ **parallel**\ . ************* Prerequisites ************* To run this tutorial you must have the following: - parallel >= version 20160822 Install the newest version using your package manager (recommended for security reasons), the way described in README, or with this command: .. code-block:: perl $ (wget -O - pi.dk/3 || lynx -source pi.dk/3 || curl pi.dk/3/ || \ fetch -o - http://pi.dk/3 ) > install.sh $ sha1sum install.sh 12345678 51621b7f 1ee103c0 0783aae4 ef9889f8 $ md5sum install.sh 62eada78 703b5500 241b8e50 baf62758 $ sha512sum install.sh 160d3159 9480cf5c a101512f 150b7ac0 206a65dc 86f2bb6b bdf1a2bc 96bc6d06 7f8237c2 0964b67f bccf8a93 332528fa 11e5ab43 2a6226a6 ceb197ab 7f03c061 $ bash install.sh This will also install the newest version of the tutorial which you can see by running this: .. code-block:: perl man parallel_tutorial Most of the tutorial will work on older versions, too. - abc-file: The file can be generated by this command: .. code-block:: perl parallel -k echo ::: A B C > abc-file - def-file: The file can be generated by this command: .. code-block:: perl parallel -k echo ::: D E F > def-file - abc0-file: The file can be generated by this command: .. code-block:: perl perl -e 'printf "A\0B\0C\0"' > abc0-file - abc_-file: The file can be generated by this command: .. code-block:: perl perl -e 'printf "A_B_C_"' > abc_-file - tsv-file.tsv The file can be generated by this command: .. code-block:: perl perl -e 'printf "f1\tf2\nA\tB\nC\tD\n"' > tsv-file.tsv - num8 The file can be generated by this command: .. code-block:: perl perl -e 'for(1..8){print "$_\n"}' > num8 - num128 The file can be generated by this command: .. code-block:: perl perl -e 'for(1..128){print "$_\n"}' > num128 - num30000 The file can be generated by this command: .. code-block:: perl perl -e 'for(1..30000){print "$_\n"}' > num30000 - num1000000 The file can be generated by this command: .. code-block:: perl perl -e 'for(1..1000000){print "$_\n"}' > num1000000 - num_%header The file can be generated by this command: .. code-block:: perl (echo %head1; echo %head2; \ perl -e 'for(1..10){print "$_\n"}') > num_%header - fixedlen The file can be generated by this command: .. code-block:: perl perl -e 'print "HHHHAAABBBCCC"' > fixedlen - For remote running: ssh login on 2 servers with no password in $SERVER1 and $SERVER2 must work. .. code-block:: perl SERVER1=server.example.com SERVER2=server2.example.net So you must be able to do this without entering a password: .. code-block:: perl ssh $SERVER1 echo works ssh $SERVER2 echo works It can be setup by running \ **ssh-keygen -t dsa; ssh-copy-id $SERVER1**\ and using an empty passphrase, or you can use \ **ssh-agent**\ . ************* Input sources ************* GNU \ **parallel**\ reads input from input sources. These can be files, the command line, and stdin (standard input or a pipe). A single input source ===================== Input can be read from the command line: .. code-block:: perl parallel echo ::: A B C Output (the order may be different because the jobs are run in parallel): .. code-block:: perl A B C The input source can be a file: .. code-block:: perl parallel -a abc-file echo Output: Same as above. STDIN (standard input) can be the input source: .. code-block:: perl cat abc-file | parallel echo Output: Same as above. Multiple input sources ====================== GNU \ **parallel**\ can take multiple input sources given on the command line. GNU \ **parallel**\ then generates all combinations of the input sources: .. code-block:: perl parallel echo ::: A B C ::: D E F Output (the order may be different): .. code-block:: perl A D A E A F B D B E B F C D C E C F The input sources can be files: .. code-block:: perl parallel -a abc-file -a def-file echo Output: Same as above. STDIN (standard input) can be one of the input sources using \ **-**\ : .. code-block:: perl cat abc-file | parallel -a - -a def-file echo Output: Same as above. Instead of \ **-a**\ files can be given after \ **::::**\ : .. code-block:: perl cat abc-file | parallel echo :::: - def-file Output: Same as above. ::: and :::: can be mixed: .. code-block:: perl parallel echo ::: A B C :::: def-file Output: Same as above. Linking arguments from input sources ------------------------------------ With \ **--link**\ you can link the input sources and get one argument from each input source: .. code-block:: perl parallel --link echo ::: A B C ::: D E F Output (the order may be different): .. code-block:: perl A D B E C F If one of the input sources is too short, its values will wrap: .. code-block:: perl parallel --link echo ::: A B C D E ::: F G Output (the order may be different): .. code-block:: perl A F B G C F D G E F For more flexible linking you can use \ **:::+**\ and \ **::::+**\ . They work like \ **:::**\ and \ **::::**\ except they link the previous input source to this input source. This will link ABC to GHI: .. code-block:: perl parallel echo :::: abc-file :::+ G H I :::: def-file Output (the order may be different): .. code-block:: perl A G D A G E A G F B H D B H E B H F C I D C I E C I F This will link GHI to DEF: .. code-block:: perl parallel echo :::: abc-file ::: G H I ::::+ def-file Output (the order may be different): .. code-block:: perl A G D A H E A I F B G D B H E B I F C G D C H E C I F If one of the input sources is too short when using \ **:::+**\ or \ **::::+**\ , the rest will be ignored: .. code-block:: perl parallel echo ::: A B C D E :::+ F G Output (the order may be different): .. code-block:: perl A F B G Changing the argument separator. ================================ GNU \ **parallel**\ can use other separators than \ **:::**\ or \ **::::**\ . This is typically useful if \ **:::**\ or \ **::::**\ is used in the command to run: .. code-block:: perl parallel --arg-sep ,, echo ,, A B C :::: def-file Output (the order may be different): .. code-block:: perl A D A E A F B D B E B F C D C E C F Changing the argument file separator: .. code-block:: perl parallel --arg-file-sep // echo ::: A B C // def-file Output: Same as above. Changing the argument delimiter =============================== GNU \ **parallel**\ will normally treat a full line as a single argument: It uses \ **\\n**\ as argument delimiter. This can be changed with \ **-d**\ : .. code-block:: perl parallel -d _ echo :::: abc_-file Output (the order may be different): .. code-block:: perl A B C NUL can be given as \ **\\0**\ : .. code-block:: perl parallel -d '\0' echo :::: abc0-file Output: Same as above. A shorthand for \ **-d '\\0'**\ is \ **-0**\ (this will often be used to read files from \ **find ... -print0**\ ): .. code-block:: perl parallel -0 echo :::: abc0-file Output: Same as above. End-of-file value for input source ================================== GNU \ **parallel**\ can stop reading when it encounters a certain value: .. code-block:: perl parallel -E stop echo ::: A B stop C D Output: .. code-block:: perl A B Skipping empty lines ==================== Using \ **--no-run-if-empty**\ GNU \ **parallel**\ will skip empty lines. .. code-block:: perl (echo 1; echo; echo 2) | parallel --no-run-if-empty echo Output: .. code-block:: perl 1 2 ************************* Building the command line ************************* No command means arguments are commands ======================================= If no command is given after parallel the arguments themselves are treated as commands: .. code-block:: perl parallel ::: ls 'echo foo' pwd Output (the order may be different): .. code-block:: perl [list of files in current dir] foo [/path/to/current/working/dir] The command can be a script, a binary or a Bash function if the function is exported using \ **export -f**\ : .. code-block:: perl # Only works in Bash my_func() { echo in my_func $1 } export -f my_func parallel my_func ::: 1 2 3 Output (the order may be different): .. code-block:: perl in my_func 1 in my_func 2 in my_func 3 Replacement strings =================== The 7 predefined replacement strings ------------------------------------ GNU \ **parallel**\ has several replacement strings. If no replacement strings are used the default is to append \ **{}**\ : .. code-block:: perl parallel echo ::: dir/file.ext dir2/file2.ext2 Output: .. code-block:: perl dir/file.ext dir2/file2.ext2 The default replacement string is \ **{}**\ : .. code-block:: perl parallel echo {} ::: dir/file.ext dir2/file2.ext2 Output: .. code-block:: perl dir/file.ext dir2/file2.ext2 The replacement string \ **{.}**\ removes the extension: .. code-block:: perl parallel echo {.} ::: dir/file.ext dir2/file2.ext2 Output: .. code-block:: perl dir/file dir2/file2 The replacement string \ **{/}**\ removes the path: .. code-block:: perl parallel echo {/} ::: dir/file.ext dir2/file2.ext2 Output: .. code-block:: perl file.ext file2.ext2 The replacement string \ **{//}**\ keeps only the path: .. code-block:: perl parallel echo {//} ::: dir/file.ext dir2/file2.ext2 Output: .. code-block:: perl dir dir2 The replacement string \ **{/.}**\ removes the path and the extension: .. code-block:: perl parallel echo {/.} ::: dir/file.ext dir2/file2.ext2 Output: .. code-block:: perl file file2 The replacement string \ **{#}**\ gives the job number: .. code-block:: perl parallel echo {#} ::: A B C Output (the order may be different): .. code-block:: perl 1 2 3 The replacement string \ **{%}**\ gives the job slot number (between 1 and number of jobs to run in parallel): .. code-block:: perl parallel -j 2 echo {%} ::: A B C Output (the order may be different and 1 and 2 may be swapped): .. code-block:: perl 1 2 1 Changing the replacement strings -------------------------------- The replacement string \ **{}**\ can be changed with \ **-I**\ : .. code-block:: perl parallel -I ,, echo ,, ::: A/B.C Output: .. code-block:: perl A/B.C The replacement string \ **{.}**\ can be changed with \ **--extensionreplace**\ : .. code-block:: perl parallel --extensionreplace ,, echo ,, ::: A/B.C Output: .. code-block:: perl A/B The replacement string \ **{/}**\ can be replaced with \ **--basenamereplace**\ : .. code-block:: perl parallel --basenamereplace ,, echo ,, ::: A/B.C Output: .. code-block:: perl B.C The replacement string \ **{//}**\ can be changed with \ **--dirnamereplace**\ : .. code-block:: perl parallel --dirnamereplace ,, echo ,, ::: A/B.C Output: .. code-block:: perl A The replacement string \ **{/.}**\ can be changed with \ **--basenameextensionreplace**\ : .. code-block:: perl parallel --basenameextensionreplace ,, echo ,, ::: A/B.C Output: .. code-block:: perl B The replacement string \ **{#}**\ can be changed with \ **--seqreplace**\ : .. code-block:: perl parallel --seqreplace ,, echo ,, ::: A B C Output (the order may be different): .. code-block:: perl 1 2 3 The replacement string \ **{%}**\ can be changed with \ **--slotreplace**\ : .. code-block:: perl parallel -j2 --slotreplace ,, echo ,, ::: A B C Output (the order may be different and 1 and 2 may be swapped): .. code-block:: perl 1 2 1 Perl expression replacement string ---------------------------------- When predefined replacement strings are not flexible enough a perl expression can be used instead. One example is to remove two extensions: foo.tar.gz becomes foo .. code-block:: perl parallel echo '{= s:\.[^.]+$::;s:\.[^.]+$::; =}' ::: foo.tar.gz Output: .. code-block:: perl foo In \ **{= =}**\ you can access all of GNU \ **parallel**\ 's internal functions and variables. A few are worth mentioning. \ **total_jobs()**\ returns the total number of jobs: .. code-block:: perl parallel echo Job {#} of {= '$_=total_jobs()' =} ::: {1..5} Output: .. code-block:: perl Job 1 of 5 Job 2 of 5 Job 3 of 5 Job 4 of 5 Job 5 of 5 \ **Q(...)**\ shell quotes the string: .. code-block:: perl parallel echo {} shell quoted is {= '$_=Q($_)' =} ::: '*/!#$' Output: .. code-block:: perl */!#$ shell quoted is \*/\!\#\$ \ **skip()**\ skips the job: .. code-block:: perl parallel echo {= 'if($_==3) { skip() }' =} ::: {1..5} Output: .. code-block:: perl 1 2 4 5 \ **@arg**\ contains the input source variables: .. code-block:: perl parallel echo {= 'if($arg[1]==$arg[2]) { skip() }' =} \ ::: {1..3} ::: {1..3} Output: .. code-block:: perl 1 2 1 3 2 1 2 3 3 1 3 2 If the strings \ **{=**\ and \ **=}**\ cause problems they can be replaced with \ **--parens**\ : .. code-block:: perl parallel --parens ,,,, echo ',, s:\.[^.]+$::;s:\.[^.]+$::; ,,' \ ::: foo.tar.gz Output: .. code-block:: perl foo To define a shorthand replacement string use \ **--rpl**\ : .. code-block:: perl parallel --rpl '.. s:\.[^.]+$::;s:\.[^.]+$::;' echo '..' \ ::: foo.tar.gz Output: Same as above. If the shorthand starts with \ **{**\ it can be used as a positional replacement string, too: .. code-block:: perl parallel --rpl '{..} s:\.[^.]+$::;s:\.[^.]+$::;' echo '{..}' ::: foo.tar.gz Output: Same as above. If the shorthand contains matching parenthesis the replacement string becomes a dynamic replacement string and the string in the parenthesis can be accessed as $$1. If there are multiple matching parenthesis, the matched strings can be accessed using $$2, $$3 and so on. You can think of this as giving arguments to the replacement string. Here we give the argument \ **.tar.gz**\ to the replacement string \ **{%\ \*string\*\ }**\ which removes \ *string*\ : .. code-block:: perl parallel --rpl '{%(.+?)} s/$$1$//;' echo {%.tar.gz}.zip ::: foo.tar.gz Output: .. code-block:: perl foo.zip Here we give the two arguments \ **tar.gz**\ and \ **zip**\ to the replacement string \ **{/\ \*string1\*\ /\ \*string2\*\ }**\ which replaces \ *string1*\ with \ *string2*\ : .. code-block:: perl parallel --rpl '{/(.+?)/(.*?)} s/$$1/$$2/;' echo {/tar.gz/zip} \ ::: foo.tar.gz Output: .. code-block:: perl foo.zip GNU \ **parallel**\ 's 7 replacement strings are implemented as this: .. code-block:: perl --rpl '{} ' --rpl '{#} $_=$job->seq()' --rpl '{%} $_=$job->slot()' --rpl '{/} s:.*/::' --rpl '{//} $Global::use{"File::Basename"} ||= eval "use File::Basename; 1;"; $_ = dirname($_);' --rpl '{/.} s:.*/::; s:\.[^/.]+$::;' --rpl '{.} s:\.[^/.]+$::' Positional replacement strings ------------------------------ With multiple input sources the argument from the individual input sources can be accessed with \ **{**\ number\ **}**\ : .. code-block:: perl parallel echo {1} and {2} ::: A B ::: C D Output (the order may be different): .. code-block:: perl A and C A and D B and C B and D The positional replacement strings can also be modified using \ **/**\ , \ **//**\ , \ **/.**\ , and \ **.**\ : .. code-block:: perl parallel echo /={1/} //={1//} /.={1/.} .={1.} ::: A/B.C D/E.F Output (the order may be different): .. code-block:: perl /=B.C //=A /.=B .=A/B /=E.F //=D /.=E .=D/E If a position is negative, it will refer to the input source counted from behind: .. code-block:: perl parallel echo 1={1} 2={2} 3={3} -1={-1} -2={-2} -3={-3} \ ::: A B ::: C D ::: E F Output (the order may be different): .. code-block:: perl 1=A 2=C 3=E -1=E -2=C -3=A 1=A 2=C 3=F -1=F -2=C -3=A 1=A 2=D 3=E -1=E -2=D -3=A 1=A 2=D 3=F -1=F -2=D -3=A 1=B 2=C 3=E -1=E -2=C -3=B 1=B 2=C 3=F -1=F -2=C -3=B 1=B 2=D 3=E -1=E -2=D -3=B 1=B 2=D 3=F -1=F -2=D -3=B Positional perl expression replacement string --------------------------------------------- To use a perl expression as a positional replacement string simply prepend the perl expression with number and space: .. code-block:: perl parallel echo '{=2 s:\.[^.]+$::;s:\.[^.]+$::; =} {1}' \ ::: bar ::: foo.tar.gz Output: .. code-block:: perl foo bar If a shorthand defined using \ **--rpl**\ starts with \ **{**\ it can be used as a positional replacement string, too: .. code-block:: perl parallel --rpl '{..} s:\.[^.]+$::;s:\.[^.]+$::;' echo '{2..} {1}' \ ::: bar ::: foo.tar.gz Output: Same as above. Input from columns ------------------ The columns in a file can be bound to positional replacement strings using \ **--colsep**\ . Here the columns are separated by TAB (\\t): .. code-block:: perl parallel --colsep '\t' echo 1={1} 2={2} :::: tsv-file.tsv Output (the order may be different): .. code-block:: perl 1=f1 2=f2 1=A 2=B 1=C 2=D Header defined replacement strings ---------------------------------- With \ **--header**\ GNU \ **parallel**\ will use the first value of the input source as the name of the replacement string. Only the non-modified version \ **{}**\ is supported: .. code-block:: perl parallel --header : echo f1={f1} f2={f2} ::: f1 A B ::: f2 C D Output (the order may be different): .. code-block:: perl f1=A f2=C f1=A f2=D f1=B f2=C f1=B f2=D It is useful with \ **--colsep**\ for processing files with TAB separated values: .. code-block:: perl parallel --header : --colsep '\t' echo f1={f1} f2={f2} \ :::: tsv-file.tsv Output (the order may be different): .. code-block:: perl f1=A f2=B f1=C f2=D More pre-defined replacement strings with --plus ------------------------------------------------ \ **--plus**\ adds the replacement strings \ **{+/} {+.} {+..} {+...} {..} {...} {/..} {/...} {##}**\ . The idea being that \ **{+foo}**\ matches the opposite of \ **{foo}**\ and \ **{}**\ = \ **{+/}**\ /\ **{/}**\ = \ **{.}**\ .\ **{+.}**\ = \ **{+/}**\ /\ **{/.}**\ .\ **{+.}**\ = \ **{..}**\ .\ **{+..}**\ = \ **{+/}**\ /\ **{/..}**\ .\ **{+..}**\ = \ **{...}**\ .\ **{+...}**\ = \ **{+/}**\ /\ **{/...}**\ .\ **{+...}**\ . .. code-block:: perl parallel --plus echo {} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {+/}/{/} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {.}.{+.} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {+/}/{/.}.{+.} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {..}.{+..} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {+/}/{/..}.{+..} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {...}.{+...} ::: dir/sub/file.ex1.ex2.ex3 parallel --plus echo {+/}/{/...}.{+...} ::: dir/sub/file.ex1.ex2.ex3 Output: .. code-block:: perl dir/sub/file.ex1.ex2.ex3 \ **{##}**\ is simply the number of jobs: .. code-block:: perl parallel --plus echo Job {#} of {##} ::: {1..5} Output: .. code-block:: perl Job 1 of 5 Job 2 of 5 Job 3 of 5 Job 4 of 5 Job 5 of 5 Dynamic replacement strings with --plus --------------------------------------- \ **--plus**\ also defines these dynamic replacement strings: - \ **{:-\ \*string\*\ }**\ Default value is \ *string*\ if the argument is empty. - \ **{:\ \*number\*\ }**\ Substring from \ *number*\ till end of string. - \ **{:\ \*number1\*\ :\ \*number2\*\ }**\ Substring from \ *number1*\ to \ *number2*\ . - \ **{#\ \*string\*\ }**\ If the argument starts with \ *string*\ , remove it. - \ **{%\ \*string\*\ }**\ If the argument ends with \ *string*\ , remove it. - \ **{/\ \*string1\*\ /\ \*string2\*\ }**\ Replace \ *string1*\ with \ *string2*\ . - \ **{^\ \*string\*\ }**\ If the argument starts with \ *string*\ , upper case it. \ *string*\ must be a single letter. - \ **{^^\ \*string\*\ }**\ If the argument contains \ *string*\ , upper case it. \ *string*\ must be a single letter. - \ **{,\ \*string\*\ }**\ If the argument starts with \ *string*\ , lower case it. \ *string*\ must be a single letter. - \ **{,,\ \*string\*\ }**\ If the argument contains \ *string*\ , lower case it. \ *string*\ must be a single letter. They are inspired from \ **Bash**\ : .. code-block:: perl unset myvar echo ${myvar:-myval} parallel --plus echo {:-myval} ::: "$myvar" myvar=abcAaAdef echo ${myvar:2} parallel --plus echo {:2} ::: "$myvar" echo ${myvar:2:3} parallel --plus echo {:2:3} ::: "$myvar" echo ${myvar#bc} parallel --plus echo {#bc} ::: "$myvar" echo ${myvar#abc} parallel --plus echo {#abc} ::: "$myvar" echo ${myvar%de} parallel --plus echo {%de} ::: "$myvar" echo ${myvar%def} parallel --plus echo {%def} ::: "$myvar" echo ${myvar/def/ghi} parallel --plus echo {/def/ghi} ::: "$myvar" echo ${myvar^a} parallel --plus echo {^a} ::: "$myvar" echo ${myvar^^a} parallel --plus echo {^^a} ::: "$myvar" myvar=AbcAaAdef echo ${myvar,A} parallel --plus echo '{,A}' ::: "$myvar" echo ${myvar,,A} parallel --plus echo '{,,A}' ::: "$myvar" Output: .. code-block:: perl myval myval cAaAdef cAaAdef cAa cAa abcAaAdef abcAaAdef AaAdef AaAdef abcAaAdef abcAaAdef abcAaA abcAaA abcAaAghi abcAaAghi AbcAaAdef AbcAaAdef AbcAAAdef AbcAAAdef abcAaAdef abcAaAdef abcaaadef abcaaadef More than one argument ====================== With \ **--xargs**\ GNU \ **parallel**\ will fit as many arguments as possible on a single line: .. code-block:: perl cat num30000 | parallel --xargs echo | wc -l Output (if you run this under Bash on GNU/Linux): .. code-block:: perl 2 The 30000 arguments fitted on 2 lines. The maximal length of a single line can be set with \ **-s**\ . With a maximal line length of 10000 chars 17 commands will be run: .. code-block:: perl cat num30000 | parallel --xargs -s 10000 echo | wc -l Output: .. code-block:: perl 17 For better parallelism GNU \ **parallel**\ can distribute the arguments between all the parallel jobs when end of file is met. Below GNU \ **parallel**\ reads the last argument when generating the second job. When GNU \ **parallel**\ reads the last argument, it spreads all the arguments for the second job over 4 jobs instead, as 4 parallel jobs are requested. The first job will be the same as the \ **--xargs**\ example above, but the second job will be split into 4 evenly sized jobs, resulting in a total of 5 jobs: .. code-block:: perl cat num30000 | parallel --jobs 4 -m echo | wc -l Output (if you run this under Bash on GNU/Linux): .. code-block:: perl 5 This is even more visible when running 4 jobs with 10 arguments. The 10 arguments are being spread over 4 jobs: .. code-block:: perl parallel --jobs 4 -m echo ::: 1 2 3 4 5 6 7 8 9 10 Output: .. code-block:: perl 1 2 3 4 5 6 7 8 9 10 A replacement string can be part of a word. \ **-m**\ will not repeat the context: .. code-block:: perl parallel --jobs 4 -m echo pre-{}-post ::: A B C D E F G Output (the order may be different): .. code-block:: perl pre-A B-post pre-C D-post pre-E F-post pre-G-post To repeat the context use \ **-X**\ which otherwise works like \ **-m**\ : .. code-block:: perl parallel --jobs 4 -X echo pre-{}-post ::: A B C D E F G Output (the order may be different): .. code-block:: perl pre-A-post pre-B-post pre-C-post pre-D-post pre-E-post pre-F-post pre-G-post To limit the number of arguments use \ **-N**\ : .. code-block:: perl parallel -N3 echo ::: A B C D E F G H Output (the order may be different): .. code-block:: perl A B C D E F G H \ **-N**\ also sets the positional replacement strings: .. code-block:: perl parallel -N3 echo 1={1} 2={2} 3={3} ::: A B C D E F G H Output (the order may be different): .. code-block:: perl 1=A 2=B 3=C 1=D 2=E 3=F 1=G 2=H 3= \ **-N0**\ reads 1 argument but inserts none: .. code-block:: perl parallel -N0 echo foo ::: 1 2 3 Output: .. code-block:: perl foo foo foo Quoting ======= Command lines that contain special characters may need to be protected from the shell. The \ **perl**\ program \ **print "@ARGV\\n"**\ basically works like \ **echo**\ . .. code-block:: perl perl -e 'print "@ARGV\n"' A Output: .. code-block:: perl A To run that in parallel the command needs to be quoted: .. code-block:: perl parallel perl -e 'print "@ARGV\n"' ::: This wont work Output: .. code-block:: perl [Nothing] To quote the command use \ **-q**\ : .. code-block:: perl parallel -q perl -e 'print "@ARGV\n"' ::: This works Output (the order may be different): .. code-block:: perl This works Or you can quote the critical part using \ **\\'**\ : .. code-block:: perl parallel perl -e \''print "@ARGV\n"'\' ::: This works, too Output (the order may be different): .. code-block:: perl This works, too GNU \ **parallel**\ can also \\-quote full lines. Simply run this: .. code-block:: perl parallel --shellquote Warning: Input is read from the terminal. You either know what you Warning: are doing (in which case: YOU ARE AWESOME!) or you forgot Warning: ::: or :::: or to pipe data into parallel. If so Warning: consider going through the tutorial: man parallel_tutorial Warning: Press CTRL-D to exit. perl -e 'print "@ARGV\n"' [CTRL-D] Output: .. code-block:: perl perl\ -e\ \'print\ \"@ARGV\\n\"\' This can then be used as the command: .. code-block:: perl parallel perl\ -e\ \'print\ \"@ARGV\\n\"\' ::: This also works Output (the order may be different): .. code-block:: perl This also works Trimming space ============== Space can be trimmed on the arguments using \ **--trim**\ : .. code-block:: perl parallel --trim r echo pre-{}-post ::: ' A ' Output: .. code-block:: perl pre- A-post To trim on the left side: .. code-block:: perl parallel --trim l echo pre-{}-post ::: ' A ' Output: .. code-block:: perl pre-A -post To trim on the both sides: .. code-block:: perl parallel --trim lr echo pre-{}-post ::: ' A ' Output: .. code-block:: perl pre-A-post Respecting the shell ==================== This tutorial uses Bash as the shell. GNU \ **parallel**\ respects which shell you are using, so in \ **zsh**\ you can do: .. code-block:: perl parallel echo \={} ::: zsh bash ls Output: .. code-block:: perl /usr/bin/zsh /bin/bash /bin/ls In \ **csh**\ you can do: .. code-block:: perl parallel 'set a="{}"; if( { test -d "$a" } ) echo "$a is a dir"' ::: * Output: .. code-block:: perl [somedir] is a dir This also becomes useful if you use GNU \ **parallel**\ in a shell script: GNU \ **parallel**\ will use the same shell as the shell script. ********************** Controlling the output ********************** The output can prefixed with the argument: .. code-block:: perl parallel --tag echo foo-{} ::: A B C Output (the order may be different): .. code-block:: perl A foo-A B foo-B C foo-C To prefix it with another string use \ **--tagstring**\ : .. code-block:: perl parallel --tagstring {}-bar echo foo-{} ::: A B C Output (the order may be different): .. code-block:: perl A-bar foo-A B-bar foo-B C-bar foo-C To see what commands will be run without running them use \ **--dryrun**\ : .. code-block:: perl parallel --dryrun echo {} ::: A B C Output (the order may be different): .. code-block:: perl echo A echo B echo C To print the command before running them use \ **--verbose**\ : .. code-block:: perl parallel --verbose echo {} ::: A B C Output (the order may be different): .. code-block:: perl echo A echo B A echo C B C GNU \ **parallel**\ will postpone the output until the command completes: .. code-block:: perl parallel -j2 'printf "%s-start\n%s" {} {}; sleep {};printf "%s\n" -middle;echo {}-end' ::: 4 2 1 Output: .. code-block:: perl 2-start 2-middle 2-end 1-start 1-middle 1-end 4-start 4-middle 4-end To get the output immediately use \ **--ungroup**\ : .. code-block:: perl parallel -j2 --ungroup 'printf "%s-start\n%s" {} {}; sleep {};printf "%s\n" -middle;echo {}-end' ::: 4 2 1 Output: .. code-block:: perl 4-start 42-start 2-middle 2-end 1-start 1-middle 1-end -middle 4-end \ **--ungroup**\ is fast, but can cause half a line from one job to be mixed with half a line of another job. That has happened in the second line, where the line '4-middle' is mixed with '2-start'. To avoid this use \ **--linebuffer**\ : .. code-block:: perl parallel -j2 --linebuffer 'printf "%s-start\n%s" {} {}; sleep {};printf "%s\n" -middle;echo {}-end' ::: 4 2 1 Output: .. code-block:: perl 4-start 2-start 2-middle 2-end 1-start 1-middle 1-end 4-middle 4-end To force the output in the same order as the arguments use \ **--keep-order**\ /\ **-k**\ : .. code-block:: perl parallel -j2 -k 'printf "%s-start\n%s" {} {}; sleep {};printf "%s\n" -middle;echo {}-end' ::: 4 2 1 Output: .. code-block:: perl 4-start 4-middle 4-end 2-start 2-middle 2-end 1-start 1-middle 1-end Saving output into files ======================== GNU \ **parallel**\ can save the output of each job into files: .. code-block:: perl parallel --files echo ::: A B C Output will be similar to this: .. code-block:: perl /tmp/pAh6uWuQCg.par /tmp/opjhZCzAX4.par /tmp/W0AT_Rph2o.par By default GNU \ **parallel**\ will cache the output in files in \ **/tmp**\ . This can be changed by setting \ **$TMPDIR**\ or \ **--tmpdir**\ : .. code-block:: perl parallel --tmpdir /var/tmp --files echo ::: A B C Output will be similar to this: .. code-block:: perl /var/tmp/N_vk7phQRc.par /var/tmp/7zA4Ccf3wZ.par /var/tmp/LIuKgF_2LP.par Or: .. code-block:: perl TMPDIR=/var/tmp parallel --files echo ::: A B C Output: Same as above. The output files can be saved in a structured way using \ **--results**\ : .. code-block:: perl parallel --results outdir echo ::: A B C Output: .. code-block:: perl A B C These files were also generated containing the standard output (stdout), standard error (stderr), and the sequence number (seq): .. code-block:: perl outdir/1/A/seq outdir/1/A/stderr outdir/1/A/stdout outdir/1/B/seq outdir/1/B/stderr outdir/1/B/stdout outdir/1/C/seq outdir/1/C/stderr outdir/1/C/stdout \ **--header :**\ will take the first value as name and use that in the directory structure. This is useful if you are using multiple input sources: .. code-block:: perl parallel --header : --results outdir echo ::: f1 A B ::: f2 C D Generated files: .. code-block:: perl outdir/f1/A/f2/C/seq outdir/f1/A/f2/C/stderr outdir/f1/A/f2/C/stdout outdir/f1/A/f2/D/seq outdir/f1/A/f2/D/stderr outdir/f1/A/f2/D/stdout outdir/f1/B/f2/C/seq outdir/f1/B/f2/C/stderr outdir/f1/B/f2/C/stdout outdir/f1/B/f2/D/seq outdir/f1/B/f2/D/stderr outdir/f1/B/f2/D/stdout The directories are named after the variables and their values. ************************* Controlling the execution ************************* Number of simultaneous jobs =========================== The number of concurrent jobs is given with \ **--jobs**\ /\ **-j**\ : .. code-block:: perl /usr/bin/time parallel -N0 -j64 sleep 1 :::: num128 With 64 jobs in parallel the 128 \ **sleep**\ s will take 2-8 seconds to run - depending on how fast your machine is. By default \ **--jobs**\ is the same as the number of CPU cores. So this: .. code-block:: perl /usr/bin/time parallel -N0 sleep 1 :::: num128 should take twice the time of running 2 jobs per CPU core: .. code-block:: perl /usr/bin/time parallel -N0 --jobs 200% sleep 1 :::: num128 \ **--jobs 0**\ will run as many jobs in parallel as possible: .. code-block:: perl /usr/bin/time parallel -N0 --jobs 0 sleep 1 :::: num128 which should take 1-7 seconds depending on how fast your machine is. \ **--jobs**\ can read from a file which is re-read when a job finishes: .. code-block:: perl echo 50% > my_jobs /usr/bin/time parallel -N0 --jobs my_jobs sleep 1 :::: num128 & sleep 1 echo 0 > my_jobs wait The first second only 50% of the CPU cores will run a job. Then \ **0**\ is put into \ **my_jobs**\ and then the rest of the jobs will be started in parallel. Instead of basing the percentage on the number of CPU cores GNU \ **parallel**\ can base it on the number of CPUs: .. code-block:: perl parallel --use-cpus-instead-of-cores -N0 sleep 1 :::: num8 Shuffle job order ================= If you have many jobs (e.g. by multiple combinations of input sources), it can be handy to shuffle the jobs, so you get different values run. Use \ **--shuf**\ for that: .. code-block:: perl parallel --shuf echo ::: 1 2 3 ::: a b c ::: A B C Output: .. code-block:: perl All combinations but different order for each run. Interactivity ============= GNU \ **parallel**\ can ask the user if a command should be run using \ **--interactive**\ : .. code-block:: perl parallel --interactive echo ::: 1 2 3 Output: .. code-block:: perl echo 1 ?...y echo 2 ?...n 1 echo 3 ?...y 3 GNU \ **parallel**\ can be used to put arguments on the command line for an interactive command such as \ **emacs**\ to edit one file at a time: .. code-block:: perl parallel --tty emacs ::: 1 2 3 Or give multiple argument in one go to open multiple files: .. code-block:: perl parallel -X --tty vi ::: 1 2 3 A terminal for every job ======================== Using \ **--tmux**\ GNU \ **parallel**\ can start a terminal for every job run: .. code-block:: perl seq 10 20 | parallel --tmux 'echo start {}; sleep {}; echo done {}' This will tell you to run something similar to: .. code-block:: perl tmux -S /tmp/tmsrPrO0 attach Using normal \ **tmux**\ keystrokes (CTRL-b n or CTRL-b p) you can cycle between windows of the running jobs. When a job is finished it will pause for 10 seconds before closing the window. Timing ====== Some jobs do heavy I/O when they start. To avoid a thundering herd GNU \ **parallel**\ can delay starting new jobs. \ **--delay**\ \ *X*\ will make sure there is at least \ *X*\ seconds between each start: .. code-block:: perl parallel --delay 2.5 echo Starting {}\;date ::: 1 2 3 Output: .. code-block:: perl Starting 1 Thu Aug 15 16:24:33 CEST 2013 Starting 2 Thu Aug 15 16:24:35 CEST 2013 Starting 3 Thu Aug 15 16:24:38 CEST 2013 If jobs taking more than a certain amount of time are known to fail, they can be stopped with \ **--timeout**\ . The accuracy of \ **--timeout**\ is 2 seconds: .. code-block:: perl parallel --timeout 4.1 sleep {}\; echo {} ::: 2 4 6 8 Output: .. code-block:: perl 2 4 GNU \ **parallel**\ can compute the median runtime for jobs and kill those that take more than 200% of the median runtime: .. code-block:: perl parallel --timeout 200% sleep {}\; echo {} ::: 2.1 2.2 3 7 2.3 Output: .. code-block:: perl 2.1 2.2 3 2.3 Progress information ==================== Based on the runtime of completed jobs GNU \ **parallel**\ can estimate the total runtime: .. code-block:: perl parallel --eta sleep ::: 1 3 2 2 1 3 3 2 1 Output: .. code-block:: perl Computers / CPU cores / Max jobs to run 1:local / 2 / 2 Computer:jobs running/jobs completed/%of started jobs/ Average seconds to complete ETA: 2s 0left 1.11avg local:0/9/100%/1.1s GNU \ **parallel**\ can give progress information with \ **--progress**\ : .. code-block:: perl parallel --progress sleep ::: 1 3 2 2 1 3 3 2 1 Output: .. code-block:: perl Computers / CPU cores / Max jobs to run 1:local / 2 / 2 Computer:jobs running/jobs completed/%of started jobs/ Average seconds to complete local:0/9/100%/1.1s A progress bar can be shown with \ **--bar**\ : .. code-block:: perl parallel --bar sleep ::: 1 3 2 2 1 3 3 2 1 And a graphic bar can be shown with \ **--bar**\ and \ **zenity**\ : .. code-block:: perl seq 1000 | parallel -j10 --bar '(echo -n {};sleep 0.1)' \ 2> >(perl -pe 'BEGIN{$/="\r";$|=1};s/\r/\n/g' | zenity --progress --auto-kill --auto-close) A logfile of the jobs completed so far can be generated with \ **--joblog**\ : .. code-block:: perl parallel --joblog /tmp/log exit ::: 1 2 3 0 cat /tmp/log Output: .. code-block:: perl Seq Host Starttime Runtime Send Receive Exitval Signal Command 1 : 1376577364.974 0.008 0 0 1 0 exit 1 2 : 1376577364.982 0.013 0 0 2 0 exit 2 3 : 1376577364.990 0.013 0 0 3 0 exit 3 4 : 1376577365.003 0.003 0 0 0 0 exit 0 The log contains the job sequence, which host the job was run on, the start time and run time, how much data was transferred, the exit value, the signal that killed the job, and finally the command being run. With a joblog GNU \ **parallel**\ can be stopped and later pickup where it left off. It it important that the input of the completed jobs is unchanged. .. code-block:: perl parallel --joblog /tmp/log exit ::: 1 2 3 0 cat /tmp/log parallel --resume --joblog /tmp/log exit ::: 1 2 3 0 0 0 cat /tmp/log Output: .. code-block:: perl Seq Host Starttime Runtime Send Receive Exitval Signal Command 1 : 1376580069.544 0.008 0 0 1 0 exit 1 2 : 1376580069.552 0.009 0 0 2 0 exit 2 3 : 1376580069.560 0.012 0 0 3 0 exit 3 4 : 1376580069.571 0.005 0 0 0 0 exit 0 Seq Host Starttime Runtime Send Receive Exitval Signal Command 1 : 1376580069.544 0.008 0 0 1 0 exit 1 2 : 1376580069.552 0.009 0 0 2 0 exit 2 3 : 1376580069.560 0.012 0 0 3 0 exit 3 4 : 1376580069.571 0.005 0 0 0 0 exit 0 5 : 1376580070.028 0.009 0 0 0 0 exit 0 6 : 1376580070.038 0.007 0 0 0 0 exit 0 Note how the start time of the last 2 jobs is clearly different from the second run. With \ **--resume-failed**\ GNU \ **parallel**\ will re-run the jobs that failed: .. code-block:: perl parallel --resume-failed --joblog /tmp/log exit ::: 1 2 3 0 0 0 cat /tmp/log Output: .. code-block:: perl Seq Host Starttime Runtime Send Receive Exitval Signal Command 1 : 1376580069.544 0.008 0 0 1 0 exit 1 2 : 1376580069.552 0.009 0 0 2 0 exit 2 3 : 1376580069.560 0.012 0 0 3 0 exit 3 4 : 1376580069.571 0.005 0 0 0 0 exit 0 5 : 1376580070.028 0.009 0 0 0 0 exit 0 6 : 1376580070.038 0.007 0 0 0 0 exit 0 1 : 1376580154.433 0.010 0 0 1 0 exit 1 2 : 1376580154.444 0.022 0 0 2 0 exit 2 3 : 1376580154.466 0.005 0 0 3 0 exit 3 Note how seq 1 2 3 have been repeated because they had exit value different from 0. \ **--retry-failed**\ does almost the same as \ **--resume-failed**\ . Where \ **--resume-failed**\ reads the commands from the command line (and ignores the commands in the joblog), \ **--retry-failed**\ ignores the command line and reruns the commands mentioned in the joblog. .. code-block:: perl parallel --retry-failed --joblog /tmp/log cat /tmp/log Output: .. code-block:: perl Seq Host Starttime Runtime Send Receive Exitval Signal Command 1 : 1376580069.544 0.008 0 0 1 0 exit 1 2 : 1376580069.552 0.009 0 0 2 0 exit 2 3 : 1376580069.560 0.012 0 0 3 0 exit 3 4 : 1376580069.571 0.005 0 0 0 0 exit 0 5 : 1376580070.028 0.009 0 0 0 0 exit 0 6 : 1376580070.038 0.007 0 0 0 0 exit 0 1 : 1376580154.433 0.010 0 0 1 0 exit 1 2 : 1376580154.444 0.022 0 0 2 0 exit 2 3 : 1376580154.466 0.005 0 0 3 0 exit 3 1 : 1376580164.633 0.010 0 0 1 0 exit 1 2 : 1376580164.644 0.022 0 0 2 0 exit 2 3 : 1376580164.666 0.005 0 0 3 0 exit 3 Termination =========== Unconditional termination ------------------------- By default GNU \ **parallel**\ will wait for all jobs to finish before exiting. If you send GNU \ **parallel**\ the \ **TERM**\ signal, GNU \ **parallel**\ will stop spawning new jobs and wait for the remaining jobs to finish. If you send GNU \ **parallel**\ the \ **TERM**\ signal again, GNU \ **parallel**\ will kill all running jobs and exit. Termination dependent on job status ----------------------------------- For certain jobs there is no need to continue if one of the jobs fails and has an exit code different from 0. GNU \ **parallel**\ will stop spawning new jobs with \ **--halt soon,fail=1**\ : .. code-block:: perl parallel -j2 --halt soon,fail=1 echo {}\; exit {} ::: 0 0 1 2 3 Output: .. code-block:: perl 0 0 1 parallel: This job failed: echo 1; exit 1 parallel: Starting no more jobs. Waiting for 1 jobs to finish. 2 With \ **--halt now,fail=1**\ the running jobs will be killed immediately: .. code-block:: perl parallel -j2 --halt now,fail=1 echo {}\; exit {} ::: 0 0 1 2 3 Output: .. code-block:: perl 0 0 1 parallel: This job failed: echo 1; exit 1 If \ **--halt**\ is given a percentage this percentage of the jobs must fail before GNU \ **parallel**\ stops spawning more jobs: .. code-block:: perl parallel -j2 --halt soon,fail=20% echo {}\; exit {} \ ::: 0 1 2 3 4 5 6 7 8 9 Output: .. code-block:: perl 0 1 parallel: This job failed: echo 1; exit 1 2 parallel: This job failed: echo 2; exit 2 parallel: Starting no more jobs. Waiting for 1 jobs to finish. 3 parallel: This job failed: echo 3; exit 3 If you are looking for success instead of failures, you can use \ **success**\ . This will finish as soon as the first job succeeds: .. code-block:: perl parallel -j2 --halt now,success=1 echo {}\; exit {} ::: 1 2 3 0 4 5 6 Output: .. code-block:: perl 1 2 3 0 parallel: This job succeeded: echo 0; exit 0 GNU \ **parallel**\ can retry the command with \ **--retries**\ . This is useful if a command fails for unknown reasons now and then. .. code-block:: perl parallel -k --retries 3 \ 'echo tried {} >>/tmp/runs; echo completed {}; exit {}' ::: 1 2 0 cat /tmp/runs Output: .. code-block:: perl completed 1 completed 2 completed 0 tried 1 tried 2 tried 1 tried 2 tried 1 tried 2 tried 0 Note how job 1 and 2 were tried 3 times, but 0 was not retried because it had exit code 0. Termination signals (advanced) ------------------------------ Using \ **--termseq**\ you can control which signals are sent when killing children. Normally children will be killed by sending them \ **SIGTERM**\ , waiting 200 ms, then another \ **SIGTERM**\ , waiting 100 ms, then another \ **SIGTERM**\ , waiting 50 ms, then a \ **SIGKILL**\ , finally waiting 25 ms before giving up. It looks like this: .. code-block:: perl show_signals() { perl -e 'for(keys %SIG) { $SIG{$_} = eval "sub { print \"Got $_\\n\"; }"; } while(1){sleep 1}' } export -f show_signals echo | parallel --termseq TERM,200,TERM,100,TERM,50,KILL,25 \ -u --timeout 1 show_signals Output: .. code-block:: perl Got TERM Got TERM Got TERM Or just: .. code-block:: perl echo | parallel -u --timeout 1 show_signals Output: Same as above. You can change this to \ **SIGINT**\ , \ **SIGTERM**\ , \ **SIGKILL**\ : .. code-block:: perl echo | parallel --termseq INT,200,TERM,100,KILL,25 \ -u --timeout 1 show_signals Output: .. code-block:: perl Got INT Got TERM The \ **SIGKILL**\ does not show because it cannot be caught, and thus the child dies. Limiting the resources ====================== To avoid overloading systems GNU \ **parallel**\ can look at the system load before starting another job: .. code-block:: perl parallel --load 100% echo load is less than {} job per cpu ::: 1 Output: .. code-block:: perl [when then load is less than the number of cpu cores] load is less than 1 job per cpu GNU \ **parallel**\ can also check if the system is swapping. .. code-block:: perl parallel --noswap echo the system is not swapping ::: now Output: .. code-block:: perl [when then system is not swapping] the system is not swapping now Some jobs need a lot of memory, and should only be started when there is enough memory free. Using \ **--memfree**\ GNU \ **parallel**\ can check if there is enough memory free. Additionally, GNU \ **parallel**\ will kill off the youngest job if the memory free falls below 50% of the size. The killed job will put back on the queue and retried later. .. code-block:: perl parallel --memfree 1G echo will run if more than 1 GB is ::: free GNU \ **parallel**\ can run the jobs with a nice value. This will work both locally and remotely. .. code-block:: perl parallel --nice 17 echo this is being run with nice -n ::: 17 Output: .. code-block:: perl this is being run with nice -n 17 **************** Remote execution **************** GNU \ **parallel**\ can run jobs on remote servers. It uses \ **ssh**\ to communicate with the remote machines. Sshlogin ======== The most basic sshlogin is \ **-S**\ \ *host*\ : .. code-block:: perl parallel -S $SERVER1 echo running on ::: $SERVER1 Output: .. code-block:: perl running on [$SERVER1] To use a different username prepend the server with \ *username@*\ : .. code-block:: perl parallel -S username@$SERVER1 echo running on ::: username@$SERVER1 Output: .. code-block:: perl running on [username@$SERVER1] The special sshlogin \ **:**\ is the local machine: .. code-block:: perl parallel -S : echo running on ::: the_local_machine Output: .. code-block:: perl running on the_local_machine If \ **ssh**\ is not in $PATH it can be prepended to $SERVER1: .. code-block:: perl parallel -S '/usr/bin/ssh '$SERVER1 echo custom ::: ssh Output: .. code-block:: perl custom ssh The \ **ssh**\ command can also be given using \ **--ssh**\ : .. code-block:: perl parallel --ssh /usr/bin/ssh -S $SERVER1 echo custom ::: ssh or by setting \ **$PARALLEL_SSH**\ : .. code-block:: perl export PARALLEL_SSH=/usr/bin/ssh parallel -S $SERVER1 echo custom ::: ssh Several servers can be given using multiple \ **-S**\ : .. code-block:: perl parallel -S $SERVER1 -S $SERVER2 echo ::: running on more hosts Output (the order may be different): .. code-block:: perl running on more hosts Or they can be separated by \ **,**\ : .. code-block:: perl parallel -S $SERVER1,$SERVER2 echo ::: running on more hosts Output: Same as above. Or newline: .. code-block:: perl # This gives a \n between $SERVER1 and $SERVER2 SERVERS="`echo $SERVER1; echo $SERVER2`" parallel -S "$SERVERS" echo ::: running on more hosts They can also be read from a file (replace \ *user@*\ with the user on \ **$SERVER2**\ ): .. code-block:: perl echo $SERVER1 > nodefile # Force 4 cores, special ssh-command, username echo 4//usr/bin/ssh user@$SERVER2 >> nodefile parallel --sshloginfile nodefile echo ::: running on more hosts Output: Same as above. Every time a job finished, the \ **--sshloginfile**\ will be re-read, so it is possible to both add and remove hosts while running. The special \ **--sshloginfile ..**\ reads from \ **~/.parallel/sshloginfile**\ . To force GNU \ **parallel**\ to treat a server having a given number of CPU cores prepend the number of core followed by \ **/**\ to the sshlogin: .. code-block:: perl parallel -S 4/$SERVER1 echo force {} cpus on server ::: 4 Output: .. code-block:: perl force 4 cpus on server Servers can be put into groups by prepending \ *@groupname*\ to the server and the group can then be selected by appending \ *@groupname*\ to the argument if using \ **--hostgroup**\ : .. code-block:: perl parallel --hostgroup -S @grp1/$SERVER1 -S @grp2/$SERVER2 echo {} \ ::: run_on_grp1@grp1 run_on_grp2@grp2 Output: .. code-block:: perl run_on_grp1 run_on_grp2 A host can be in multiple groups by separating the groups with \ **+**\ , and you can force GNU \ **parallel**\ to limit the groups on which the command can be run with \ **-S**\ \ *@groupname*\ : .. code-block:: perl parallel -S @grp1 -S @grp1+grp2/$SERVER1 -S @grp2/SERVER2 echo {} \ ::: run_on_grp1 also_grp1 Output: .. code-block:: perl run_on_grp1 also_grp1 Transferring files ================== GNU \ **parallel**\ can transfer the files to be processed to the remote host. It does that using rsync. .. code-block:: perl echo This is input_file > input_file parallel -S $SERVER1 --transferfile {} cat ::: input_file Output: .. code-block:: perl This is input_file If the files are processed into another file, the resulting file can be transferred back: .. code-block:: perl echo This is input_file > input_file parallel -S $SERVER1 --transferfile {} --return {}.out \ cat {} ">"{}.out ::: input_file cat input_file.out Output: Same as above. To remove the input and output file on the remote server use \ **--cleanup**\ : .. code-block:: perl echo This is input_file > input_file parallel -S $SERVER1 --transferfile {} --return {}.out --cleanup \ cat {} ">"{}.out ::: input_file cat input_file.out Output: Same as above. There is a shorthand for \ **--transferfile {} --return --cleanup**\ called \ **--trc**\ : .. code-block:: perl echo This is input_file > input_file parallel -S $SERVER1 --trc {}.out cat {} ">"{}.out ::: input_file cat input_file.out Output: Same as above. Some jobs need a common database for all jobs. GNU \ **parallel**\ can transfer that using \ **--basefile**\ which will transfer the file before the first job: .. code-block:: perl echo common data > common_file parallel --basefile common_file -S $SERVER1 \ cat common_file\; echo {} ::: foo Output: .. code-block:: perl common data foo To remove it from the remote host after the last job use \ **--cleanup**\ . Working dir =========== The default working dir on the remote machines is the login dir. This can be changed with \ **--workdir**\ \ *mydir*\ . Files transferred using \ **--transferfile**\ and \ **--return**\ will be relative to \ *mydir*\ on remote computers, and the command will be executed in the dir \ *mydir*\ . The special \ *mydir*\ value \ **...**\ will create working dirs under \ **~/.parallel/tmp**\ on the remote computers. If \ **--cleanup**\ is given these dirs will be removed. The special \ *mydir*\ value \ **.**\ uses the current working dir. If the current working dir is beneath your home dir, the value \ **.**\ is treated as the relative path to your home dir. This means that if your home dir is different on remote computers (e.g. if your login is different) the relative path will still be relative to your home dir. .. code-block:: perl parallel -S $SERVER1 pwd ::: "" parallel --workdir . -S $SERVER1 pwd ::: "" parallel --workdir ... -S $SERVER1 pwd ::: "" Output: .. code-block:: perl [the login dir on $SERVER1] [current dir relative on $SERVER1] [a dir in ~/.parallel/tmp/...] Avoid overloading sshd ====================== If many jobs are started on the same server, \ **sshd**\ can be overloaded. GNU \ **parallel**\ can insert a delay between each job run on the same server: .. code-block:: perl parallel -S $SERVER1 --sshdelay 0.2 echo ::: 1 2 3 Output (the order may be different): .. code-block:: perl 1 2 3 \ **sshd**\ will be less overloaded if using \ **--controlmaster**\ , which will multiplex ssh connections: .. code-block:: perl parallel --controlmaster -S $SERVER1 echo ::: 1 2 3 Output: Same as above. Ignore hosts that are down ========================== In clusters with many hosts a few of them are often down. GNU \ **parallel**\ can ignore those hosts. In this case the host 173.194.32.46 is down: .. code-block:: perl parallel --filter-hosts -S 173.194.32.46,$SERVER1 echo ::: bar Output: .. code-block:: perl bar Running the same commands on all hosts ====================================== GNU \ **parallel**\ can run the same command on all the hosts: .. code-block:: perl parallel --onall -S $SERVER1,$SERVER2 echo ::: foo bar Output (the order may be different): .. code-block:: perl foo bar foo bar Often you will just want to run a single command on all hosts with out arguments. \ **--nonall**\ is a no argument \ **--onall**\ : .. code-block:: perl parallel --nonall -S $SERVER1,$SERVER2 echo foo bar Output: .. code-block:: perl foo bar foo bar When \ **--tag**\ is used with \ **--nonall**\ and \ **--onall**\ the \ **--tagstring**\ is the host: .. code-block:: perl parallel --nonall --tag -S $SERVER1,$SERVER2 echo foo bar Output (the order may be different): .. code-block:: perl $SERVER1 foo bar $SERVER2 foo bar \ **--jobs**\ sets the number of servers to log in to in parallel. Transferring environment variables and functions ================================================ \ **env_parallel**\ is a shell function that transfers all aliases, functions, variables, and arrays. You active it by running: .. code-block:: perl source `which env_parallel.bash` Replace \ **bash**\ with the shell you use. Now you can use \ **env_parallel**\ instead of \ **parallel**\ and still have your environment: .. code-block:: perl alias myecho=echo myvar="Joe's var is" env_parallel -S $SERVER1 'myecho $myvar' ::: green Output: .. code-block:: perl Joe's var is green The disadvantage is that if your environment is huge \ **env_parallel**\ will fail. When \ **env_parallel**\ fails, you can still use \ **--env**\ to tell GNU \ **parallel**\ to transfer an environment variable to the remote system. .. code-block:: perl MYVAR='foo bar' export MYVAR parallel --env MYVAR -S $SERVER1 echo '$MYVAR' ::: baz Output: .. code-block:: perl foo bar baz This works for functions, too, if your shell is Bash: .. code-block:: perl # This only works in Bash my_func() { echo in my_func $1 } export -f my_func parallel --env my_func -S $SERVER1 my_func ::: baz Output: .. code-block:: perl in my_func baz GNU \ **parallel**\ can copy all user defined variables and functions to the remote system. It just needs to record which ones to ignore in \ **~/.parallel/ignored_vars**\ . Do that by running this once: .. code-block:: perl parallel --record-env cat ~/.parallel/ignored_vars Output: .. code-block:: perl [list of variables to ignore - including $PATH and $HOME] Now all other variables and functions defined will be copied when using \ **--env _**\ . .. code-block:: perl # The function is only copied if using Bash my_func2() { echo in my_func2 $VAR $1 } export -f my_func2 VAR=foo export VAR parallel --env _ -S $SERVER1 'echo $VAR; my_func2' ::: bar Output: .. code-block:: perl foo in my_func2 foo bar If you use \ **env_parallel**\ the variables, functions, and aliases do not even need to be exported to be copied: .. code-block:: perl NOT='not exported var' alias myecho=echo not_ex() { myecho in not_exported_func $NOT $1 } env_parallel --env _ -S $SERVER1 'echo $NOT; not_ex' ::: bar Output: .. code-block:: perl not exported var in not_exported_func not exported var bar Showing what is actually run ============================ \ **--verbose**\ will show the command that would be run on the local machine. When using \ **--cat**\ , \ **--pipepart**\ , or when a job is run on a remote machine, the command is wrapped with helper scripts. \ **-vv**\ shows all of this. .. code-block:: perl parallel -vv --pipepart --block 1M wc :::: num30000 Output: .. code-block:: perl 131072 ? 131072 : $left))){ $left -= $read; syswrite(STDOUT,$buf); } }' 0 0 0 168894 | (wc) 30000 30000 168894 When the command gets more complex, the output is so hard to read, that it is only useful for debugging: .. code-block:: perl my_func3() { echo in my_func $1 > $1.out } export -f my_func3 parallel -vv --workdir ... --nice 17 --env _ --trc {}.out \ -S $SERVER1 my_func3 {} ::: abc-file Output will be similar to: .. code-block:: perl ( ssh server -- mkdir -p ./.parallel/tmp/aspire-1928520-1;rsync --protocol 30 -rlDzR -essh ./abc-file server:./.parallel/tmp/aspire-1928520-1 );ssh server -- exec perl -e \''@GNU_Parallel=("use","IPC::Open3;","use","MIME::Base64"); eval"@GNU_Parallel";my$eval=decode_base64(join"",@ARGV);eval$eval;'\' c3lzdGVtKCJta2RpciIsIi1wIiwiLS0iLCIucGFyYWxsZWwvdG1wL2FzcGlyZS0xOTI4N TsgY2hkaXIgIi5wYXJhbGxlbC90bXAvYXNwaXJlLTE5Mjg1MjAtMSIgfHxwcmludChTVE BhcmFsbGVsOiBDYW5ub3QgY2hkaXIgdG8gLnBhcmFsbGVsL3RtcC9hc3BpcmUtMTkyODU iKSAmJiBleGl0IDI1NTskRU5WeyJPTERQV0QifT0iL2hvbWUvdGFuZ2UvcHJpdmF0L3Bh IjskRU5WeyJQQVJBTExFTF9QSUQifT0iMTkyODUyMCI7JEVOVnsiUEFSQUxMRUxfU0VRI 0BiYXNoX2Z1bmN0aW9ucz1xdyhteV9mdW5jMyk7IGlmKCRFTlZ7IlNIRUxMIn09fi9jc2 ByaW50IFNUREVSUiAiQ1NIL1RDU0ggRE8gTk9UIFNVUFBPUlQgbmV3bGluZXMgSU4gVkF TL0ZVTkNUSU9OUy4gVW5zZXQgQGJhc2hfZnVuY3Rpb25zXG4iOyBleGVjICJmYWxzZSI7 YXNoZnVuYyA9ICJteV9mdW5jMygpIHsgIGVjaG8gaW4gbXlfZnVuYyBcJDEgPiBcJDEub Xhwb3J0IC1mIG15X2Z1bmMzID4vZGV2L251bGw7IjtAQVJHVj0ibXlfZnVuYzMgYWJjLW RzaGVsbD0iJEVOVntTSEVMTH0iOyR0bXBkaXI9Ii90bXAiOyRuaWNlPTE3O2RveyRFTlZ MRUxfVE1QfT0kdG1wZGlyLiIvcGFyIi5qb2luIiIsbWFweygwLi45LCJhIi4uInoiLCJB KVtyYW5kKDYyKV19KDEuLjUpO313aGlsZSgtZSRFTlZ7UEFSQUxMRUxfVE1QfSk7JFNJ fT1zdWJ7JGRvbmU9MTt9OyRwaWQ9Zm9yazt1bmxlc3MoJHBpZCl7c2V0cGdycDtldmFse W9yaXR5KDAsMCwkbmljZSl9O2V4ZWMkc2hlbGwsIi1jIiwoJGJhc2hmdW5jLiJAQVJHVi JleGVjOiQhXG4iO31kb3skcz0kczwxPzAuMDAxKyRzKjEuMDM6JHM7c2VsZWN0KHVuZGV mLHVuZGVmLCRzKTt9dW50aWwoJGRvbmV8fGdldHBwaWQ9PTEpO2tpbGwoU0lHSFVQLC0k dW5sZXNzJGRvbmU7d2FpdDtleGl0KCQ/JjEyNz8xMjgrKCQ/JjEyNyk6MSskPz4+OCk=; _EXIT_status=$?; mkdir -p ./.; rsync --protocol 30 --rsync-path=cd\ ./.parallel/tmp/aspire-1928520-1/./.\;\ rsync -rlDzR -essh server:./abc-file.out ./.;ssh server -- \(rm\ -f\ ./.parallel/tmp/aspire-1928520-1/abc-file\;\ sh\ -c\ \'rmdir\ ./.parallel/tmp/aspire-1928520-1/\ ./.parallel/tmp/\ ./.parallel/\ 2\>/dev/null\'\;rm\ -rf\ ./.parallel/tmp/aspire-1928520-1\;\);ssh server -- \(rm\ -f\ ./.parallel/tmp/aspire-1928520-1/abc-file.out\;\ sh\ -c\ \'rmdir\ ./.parallel/tmp/aspire-1928520-1/\ ./.parallel/tmp/\ ./.parallel/\ 2\>/dev/null\'\;rm\ -rf\ ./.parallel/tmp/aspire-1928520-1\;\);ssh server -- rm -rf .parallel/tmp/aspire-1928520-1; exit $_EXIT_status; ******************************************* Saving output to shell variables (advanced) ******************************************* GNU \ **parset**\ will set shell variables to the output of GNU \ **parallel**\ . GNU \ **parset**\ has one important limitation: It cannot be part of a pipe. In particular this means it cannot read anything from standard input (stdin) or pipe output to another program. To use GNU \ **parset**\ prepend command with destination variables: .. code-block:: perl parset myvar1,myvar2 echo ::: a b echo $myvar1 echo $myvar2 Output: .. code-block:: perl a b If you only give a single variable, it will be treated as an array: .. code-block:: perl parset myarray seq {} 5 ::: 1 2 3 echo "${myarray[1]}" Output: .. code-block:: perl 2 3 4 5 The commands to run can be an array: .. code-block:: perl cmd=("echo '<>'" "pwd") parset data ::: "${cmd[@]}" echo "${data[0]}" echo "${data[1]}" Output: .. code-block:: perl <> [current dir] ******************************** Saving to an SQL base (advanced) ******************************** GNU \ **parallel**\ can save into an SQL base. Point GNU \ **parallel**\ to a table and it will put the joblog there together with the variables and the output each in their own column. CSV as SQL base =============== The simplest is to use a CSV file as the storage table: .. code-block:: perl parallel --sqlandworker csv:///%2Ftmp/log.csv \ seq ::: 10 ::: 12 13 14 cat /tmp/log.csv Note how '/' in the path must be written as %2F. Output will be similar to: .. code-block:: perl Seq,Host,Starttime,JobRuntime,Send,Receive,Exitval,_Signal, Command,V1,V2,Stdout,Stderr 1,:,1458254498.254,0.069,0,9,0,0,"seq 10 12",10,12,"10 11 12 ", 2,:,1458254498.278,0.080,0,12,0,0,"seq 10 13",10,13,"10 11 12 13 ", 3,:,1458254498.301,0.083,0,15,0,0,"seq 10 14",10,14,"10 11 12 13 14 ", A proper CSV reader (like LibreOffice or R's read.csv) will read this format correctly - even with fields containing newlines as above. If the output is big you may want to put it into files using \ **--results**\ : .. code-block:: perl parallel --results outdir --sqlandworker csv:///%2Ftmp/log2.csv \ seq ::: 10 ::: 12 13 14 cat /tmp/log2.csv Output will be similar to: .. code-block:: perl Seq,Host,Starttime,JobRuntime,Send,Receive,Exitval,_Signal, Command,V1,V2,Stdout,Stderr 1,:,1458824738.287,0.029,0,9,0,0, "seq 10 12",10,12,outdir/1/10/2/12/stdout,outdir/1/10/2/12/stderr 2,:,1458824738.298,0.025,0,12,0,0, "seq 10 13",10,13,outdir/1/10/2/13/stdout,outdir/1/10/2/13/stderr 3,:,1458824738.309,0.026,0,15,0,0, "seq 10 14",10,14,outdir/1/10/2/14/stdout,outdir/1/10/2/14/stderr DBURL as table ============== The CSV file is an example of a DBURL. GNU \ **parallel**\ uses a DBURL to address the table. A DBURL has this format: .. code-block:: perl vendor://[[user][:password]@][host][:port]/[database[/table] Example: .. code-block:: perl mysql://scott:tiger@my.example.com/mydatabase/mytable postgresql://scott:tiger@pg.example.com/mydatabase/mytable sqlite3:///%2Ftmp%2Fmydatabase/mytable csv:///%2Ftmp/log.csv To refer to \ **/tmp/mydatabase**\ with \ **sqlite**\ or \ **csv**\ you need to encode the \ **/**\ as \ **%2F**\ . Run a job using \ **sqlite**\ on \ **mytable**\ in \ **/tmp/mydatabase**\ : .. code-block:: perl DBURL=sqlite3:///%2Ftmp%2Fmydatabase DBURLTABLE=$DBURL/mytable parallel --sqlandworker $DBURLTABLE echo ::: foo bar ::: baz quuz To see the result: .. code-block:: perl sql $DBURL 'SELECT * FROM mytable ORDER BY Seq;' Output will be similar to: .. code-block:: perl Seq|Host|Starttime|JobRuntime|Send|Receive|Exitval|_Signal| Command|V1|V2|Stdout|Stderr 1|:|1451619638.903|0.806||8|0|0|echo foo baz|foo|baz|foo baz | 2|:|1451619639.265|1.54||9|0|0|echo foo quuz|foo|quuz|foo quuz | 3|:|1451619640.378|1.43||8|0|0|echo bar baz|bar|baz|bar baz | 4|:|1451619641.473|0.958||9|0|0|echo bar quuz|bar|quuz|bar quuz | The first columns are well known from \ **--joblog**\ . \ **V1**\ and \ **V2**\ are data from the input sources. \ **Stdout**\ and \ **Stderr**\ are standard output and standard error, respectively. Using multiple workers ====================== Using an SQL base as storage costs overhead in the order of 1 second per job. One of the situations where it makes sense is if you have multiple workers. You can then have a single master machine that submits jobs to the SQL base (but does not do any of the work): .. code-block:: perl parallel --sqlmaster $DBURLTABLE echo ::: foo bar ::: baz quuz On the worker machines you run exactly the same command except you replace \ **--sqlmaster**\ with \ **--sqlworker**\ . .. code-block:: perl parallel --sqlworker $DBURLTABLE echo ::: foo bar ::: baz quuz To run a master and a worker on the same machine use \ **--sqlandworker**\ as shown earlier. ****** --pipe ****** The \ **--pipe**\ functionality puts GNU \ **parallel**\ in a different mode: Instead of treating the data on stdin (standard input) as arguments for a command to run, the data will be sent to stdin (standard input) of the command. The typical situation is: .. code-block:: perl command_A | command_B | command_C where command_B is slow, and you want to speed up command_B. Chunk size ========== By default GNU \ **parallel**\ will start an instance of command_B, read a chunk of 1 MB, and pass that to the instance. Then start another instance, read another chunk, and pass that to the second instance. .. code-block:: perl cat num1000000 | parallel --pipe wc Output (the order may be different): .. code-block:: perl 165668 165668 1048571 149797 149797 1048579 149796 149796 1048572 149797 149797 1048579 149797 149797 1048579 149796 149796 1048572 85349 85349 597444 The size of the chunk is not exactly 1 MB because GNU \ **parallel**\ only passes full lines - never half a line, thus the blocksize is only 1 MB on average. You can change the block size to 2 MB with \ **--block**\ : .. code-block:: perl cat num1000000 | parallel --pipe --block 2M wc Output (the order may be different): .. code-block:: perl 315465 315465 2097150 299593 299593 2097151 299593 299593 2097151 85349 85349 597444 GNU \ **parallel**\ treats each line as a record. If the order of records is unimportant (e.g. you need all lines processed, but you do not care which is processed first), then you can use \ **--roundrobin**\ . Without \ **--roundrobin**\ GNU \ **parallel**\ will start a command per block; with \ **--roundrobin**\ only the requested number of jobs will be started (\ **--jobs**\ ). The records will then be distributed between the running jobs: .. code-block:: perl cat num1000000 | parallel --pipe -j4 --roundrobin wc Output will be similar to: .. code-block:: perl 149797 149797 1048579 299593 299593 2097151 315465 315465 2097150 235145 235145 1646016 One of the 4 instances got a single record, 2 instances got 2 full records each, and one instance got 1 full and 1 partial record. Records ======= GNU \ **parallel**\ sees the input as records. The default record is a single line. Using \ **-N140000**\ GNU \ **parallel**\ will read 140000 records at a time: .. code-block:: perl cat num1000000 | parallel --pipe -N140000 wc Output (the order may be different): .. code-block:: perl 140000 140000 868895 140000 140000 980000 140000 140000 980000 140000 140000 980000 140000 140000 980000 140000 140000 980000 140000 140000 980000 20000 20000 140001 Note how that the last job could not get the full 140000 lines, but only 20000 lines. If a record is 75 lines \ **-L**\ can be used: .. code-block:: perl cat num1000000 | parallel --pipe -L75 wc Output (the order may be different): .. code-block:: perl 165600 165600 1048095 149850 149850 1048950 149775 149775 1048425 149775 149775 1048425 149850 149850 1048950 149775 149775 1048425 85350 85350 597450 25 25 176 Note how GNU \ **parallel**\ still reads a block of around 1 MB; but instead of passing full lines to \ **wc**\ it passes full 75 lines at a time. This of course does not hold for the last job (which in this case got 25 lines). Fixed length records ==================== Fixed length records can be processed by setting \ **--recend ''**\ and \ **--block \ \*recordsize\*\ **\ . A header of size \ *n*\ can be processed with \ **--header .{\ \*n\*\ }**\ . Here is how to process a file with a 4-byte header and a 3-byte record size: .. code-block:: perl cat fixedlen | parallel --pipe --header .{4} --block 3 --recend '' \ 'echo start; cat; echo' Output: .. code-block:: perl start HHHHAAA start HHHHCCC start HHHHBBB It may be more efficient to increase \ **--block**\ to a multiplum of the record size. Record separators ================= GNU \ **parallel**\ uses separators to determine where two records split. \ **--recstart**\ gives the string that starts a record; \ **--recend**\ gives the string that ends a record. The default is \ **--recend '\\n'**\ (newline). If both \ **--recend**\ and \ **--recstart**\ are given, then the record will only split if the recend string is immediately followed by the recstart string. Here the \ **--recend**\ is set to \ **', '**\ : .. code-block:: perl echo /foo, bar/, /baz, qux/, | \ parallel -kN1 --recend ', ' --pipe echo JOB{#}\;cat\;echo END Output: .. code-block:: perl JOB1 /foo, END JOB2 bar/, END JOB3 /baz, END JOB4 qux/, END Here the \ **--recstart**\ is set to \ **/**\ : .. code-block:: perl echo /foo, bar/, /baz, qux/, | \ parallel -kN1 --recstart / --pipe echo JOB{#}\;cat\;echo END Output: .. code-block:: perl JOB1 /foo, barEND JOB2 /, END JOB3 /baz, quxEND JOB4 /, END Here both \ **--recend**\ and \ **--recstart**\ are set: .. code-block:: perl echo /foo, bar/, /baz, qux/, | \ parallel -kN1 --recend ', ' --recstart / --pipe \ echo JOB{#}\;cat\;echo END Output: .. code-block:: perl JOB1 /foo, bar/, END JOB2 /baz, qux/, END Note the difference between setting one string and setting both strings. With \ **--regexp**\ the \ **--recend**\ and \ **--recstart**\ will be treated as a regular expression: .. code-block:: perl echo foo,bar,_baz,__qux, | \ parallel -kN1 --regexp --recend ,_+ --pipe \ echo JOB{#}\;cat\;echo END Output: .. code-block:: perl JOB1 foo,bar,_END JOB2 baz,__END JOB3 qux, END GNU \ **parallel**\ can remove the record separators with \ **--remove-rec-sep**\ /\ **--rrs**\ : .. code-block:: perl echo foo,bar,_baz,__qux, | \ parallel -kN1 --rrs --regexp --recend ,_+ --pipe \ echo JOB{#}\;cat\;echo END Output: .. code-block:: perl JOB1 foo,barEND JOB2 bazEND JOB3 qux, END Header ====== If the input data has a header, the header can be repeated for each job by matching the header with \ **--header**\ . If headers start with \ **%**\ you can do this: .. code-block:: perl cat num_%header | \ parallel --header '(%.*\n)*' --pipe -N3 echo JOB{#}\;cat Output (the order may be different): .. code-block:: perl JOB1 %head1 %head2 1 2 3 JOB2 %head1 %head2 4 5 6 JOB3 %head1 %head2 7 8 9 JOB4 %head1 %head2 10 If the header is 2 lines, \ **--header**\ 2 will work: .. code-block:: perl cat num_%header | parallel --header 2 --pipe -N3 echo JOB{#}\;cat Output: Same as above. --pipepart ========== \ **--pipe**\ is not very efficient. It maxes out at around 500 MB/s. \ **--pipepart**\ can easily deliver 5 GB/s. But there are a few limitations. The input has to be a normal file (not a pipe) given by \ **-a**\ or \ **::::**\ and \ **-L**\ /\ **-l**\ /\ **-N**\ do not work. \ **--recend**\ and \ **--recstart**\ , however, \ *do*\ work, and records can often be split on that alone. .. code-block:: perl parallel --pipepart -a num1000000 --block 3m wc Output (the order may be different): .. code-block:: perl 444443 444444 3000002 428572 428572 3000004 126985 126984 888890 ******* Shebang ******* Input data and parallel command in the same file ================================================ GNU \ **parallel**\ is often called as this: .. code-block:: perl cat input_file | parallel command With \ **--shebang**\ the \ *input_file*\ and \ **parallel**\ can be combined into the same script. UNIX shell scripts start with a shebang line like this: .. code-block:: perl #!/bin/bash GNU \ **parallel**\ can do that, too. With \ **--shebang**\ the arguments can be listed in the file. The \ **parallel**\ command is the first line of the script: .. code-block:: perl #!/usr/bin/parallel --shebang -r echo foo bar baz Output (the order may be different): .. code-block:: perl foo bar baz Parallelizing existing scripts ============================== GNU \ **parallel**\ is often called as this: .. code-block:: perl cat input_file | parallel command parallel command ::: foo bar If \ **command**\ is a script, \ **parallel**\ can be combined into a single file so this will run the script in parallel: .. code-block:: perl cat input_file | command command foo bar This \ **perl**\ script \ **perl_echo**\ works like \ **echo**\ : .. code-block:: perl #!/usr/bin/perl print "@ARGV\n" It can be called as this: .. code-block:: perl parallel perl_echo ::: foo bar By changing the \ **#!**\ -line it can be run in parallel: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/perl print "@ARGV\n" Thus this will work: .. code-block:: perl perl_echo foo bar Output (the order may be different): .. code-block:: perl foo bar This technique can be used for: - Perl: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/perl print "Arguments @ARGV\n"; - Python: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/python import sys print 'Arguments', str(sys.argv) - Bash/sh/zsh/Korn shell: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /bin/bash echo Arguments "$@" - csh: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /bin/csh echo Arguments "$argv" - Tcl: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/tclsh puts "Arguments $argv" - R: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/Rscript --vanilla --slave args <- commandArgs(trailingOnly = TRUE) print(paste("Arguments ",args)) - GNUplot: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap ARG={} /usr/bin/gnuplot print "Arguments ", system('echo $ARG') - Ruby: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/ruby print "Arguments " puts ARGV - Octave: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/octave printf ("Arguments"); arg_list = argv (); for i = 1:nargin printf (" %s", arg_list{i}); endfor printf ("\n"); - Common LISP: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/clisp (format t "~&~S~&" 'Arguments) (format t "~&~S~&" *args*) - PHP: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/php - Node.js: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/node var myArgs = process.argv.slice(2); console.log('Arguments ', myArgs); - LUA: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap /usr/bin/lua io.write "Arguments" for a = 1, #arg do io.write(" ") io.write(arg[a]) end print("") - C#: .. code-block:: perl #!/usr/bin/parallel --shebang-wrap ARGV={} /usr/bin/csharp var argv = Environment.GetEnvironmentVariable("ARGV"); print("Arguments "+argv); ********* Semaphore ********* GNU \ **parallel**\ can work as a counting semaphore. This is slower and less efficient than its normal mode. A counting semaphore is like a row of toilets. People needing a toilet can use any toilet, but if there are more people than toilets, they will have to wait for one of the toilets to become available. An alias for \ **parallel --semaphore**\ is \ **sem**\ . \ **sem**\ will follow a person to the toilets, wait until a toilet is available, leave the person in the toilet and exit. \ **sem --fg**\ will follow a person to the toilets, wait until a toilet is available, stay with the person in the toilet and exit when the person exits. \ **sem --wait**\ will wait for all persons to leave the toilets. \ **sem**\ does not have a queue discipline, so the next person is chosen randomly. \ **-j**\ sets the number of toilets. Mutex ===== The default is to have only one toilet (this is called a mutex). The program is started in the background and \ **sem**\ exits immediately. Use \ **--wait**\ to wait for all \ **sem**\ s to finish: .. code-block:: perl sem 'sleep 1; echo The first finished' && echo The first is now running in the background && sem 'sleep 1; echo The second finished' && echo The second is now running in the background sem --wait Output: .. code-block:: perl The first is now running in the background The first finished The second is now running in the background The second finished The command can be run in the foreground with \ **--fg**\ , which will only exit when the command completes: .. code-block:: perl sem --fg 'sleep 1; echo The first finished' && echo The first finished running in the foreground && sem --fg 'sleep 1; echo The second finished' && echo The second finished running in the foreground sem --wait The difference between this and just running the command, is that a mutex is set, so if other \ **sem**\ s were running in the background only one would run at a time. To control which semaphore is used, use \ **--semaphorename**\ /\ **--id**\ . Run this in one terminal: .. code-block:: perl sem --id my_id -u 'echo First started; sleep 10; echo First done' and simultaneously this in another terminal: .. code-block:: perl sem --id my_id -u 'echo Second started; sleep 10; echo Second done' Note how the second will only be started when the first has finished. Counting semaphore ================== A mutex is like having a single toilet: When it is in use everyone else will have to wait. A counting semaphore is like having multiple toilets: Several people can use the toilets, but when they all are in use, everyone else will have to wait. \ **sem**\ can emulate a counting semaphore. Use \ **--jobs**\ to set the number of toilets like this: .. code-block:: perl sem --jobs 3 --id my_id -u 'echo Start 1; sleep 5; echo 1 done' && sem --jobs 3 --id my_id -u 'echo Start 2; sleep 6; echo 2 done' && sem --jobs 3 --id my_id -u 'echo Start 3; sleep 7; echo 3 done' && sem --jobs 3 --id my_id -u 'echo Start 4; sleep 8; echo 4 done' && sem --wait --id my_id Output: .. code-block:: perl Start 1 Start 2 Start 3 1 done Start 4 2 done 3 done 4 done Timeout ======= With \ **--semaphoretimeout**\ you can force running the command anyway after a period (positive number) or give up (negative number): .. code-block:: perl sem --id foo -u 'echo Slow started; sleep 5; echo Slow ended' && sem --id foo --semaphoretimeout 1 'echo Forced running after 1 sec' && sem --id foo --semaphoretimeout -2 'echo Give up after 2 secs' sem --id foo --wait Output: .. code-block:: perl Slow started parallel: Warning: Semaphore timed out. Stealing the semaphore. Forced running after 1 sec parallel: Warning: Semaphore timed out. Exiting. Slow ended Note how the 'Give up' was not run. ************* Informational ************* GNU \ **parallel**\ has some options to give short information about the configuration. \ **--help**\ will print a summary of the most important options: .. code-block:: perl parallel --help Output: .. code-block:: perl Usage: parallel [options] [command [arguments]] < list_of_arguments parallel [options] [command [arguments]] (::: arguments|:::: argfile(s))... cat ... | parallel --pipe [options] [command [arguments]] -j n Run n jobs in parallel -k Keep same order -X Multiple arguments with context replace --colsep regexp Split input on regexp for positional replacements {} {.} {/} {/.} {#} {%} {= perl code =} Replacement strings {3} {3.} {3/} {3/.} {=3 perl code =} Positional replacement strings With --plus: {} = {+/}/{/} = {.}.{+.} = {+/}/{/.}.{+.} = {..}.{+..} = {+/}/{/..}.{+..} = {...}.{+...} = {+/}/{/...}.{+...} -S sshlogin Example: foo@server.example.com --slf .. Use ~/.parallel/sshloginfile as the list of sshlogins --trc {}.bar Shorthand for --transfer --return {}.bar --cleanup --onall Run the given command with argument on all sshlogins --nonall Run the given command with no arguments on all sshlogins --pipe Split stdin (standard input) to multiple jobs. --recend str Record end separator for --pipe. --recstart str Record start separator for --pipe. See 'man parallel' for details Academic tradition requires you to cite works you base your article on. When using programs that use GNU Parallel to process data for publication please cite: O. Tange (2011): GNU Parallel - The Command-Line Power Tool, ;login: The USENIX Magazine, February 2011:42-47. This helps funding further development; AND IT WON'T COST YOU A CENT. If you pay 10000 EUR you should feel free to use GNU Parallel without citing. When asking for help, always report the full output of this: .. code-block:: perl parallel --version Output: .. code-block:: perl GNU parallel 20230122 Copyright (C) 2007-2024 Ole Tange, http://ole.tange.dk and Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. GNU parallel comes with no warranty. Web site: https://www.gnu.org/software/parallel When using programs that use GNU Parallel to process data for publication please cite as described in 'parallel --citation'. In scripts \ **--minversion**\ can be used to ensure the user has at least this version: .. code-block:: perl parallel --minversion 20130722 && \ echo Your version is at least 20130722. Output: .. code-block:: perl 20160322 Your version is at least 20130722. If you are using GNU \ **parallel**\ for research the BibTeX citation can be generated using \ **--citation**\ : .. code-block:: perl parallel --citation Output: .. code-block:: perl Academic tradition requires you to cite works you base your article on. When using programs that use GNU Parallel to process data for publication please cite: @article{Tange2011a, title = {GNU Parallel - The Command-Line Power Tool}, author = {O. Tange}, address = {Frederiksberg, Denmark}, journal = {;login: The USENIX Magazine}, month = {Feb}, number = {1}, volume = {36}, url = {https://www.gnu.org/s/parallel}, year = {2011}, pages = {42-47}, doi = {10.5281/zenodo.16303} } (Feel free to use \nocite{Tange2011a}) This helps funding further development; AND IT WON'T COST YOU A CENT. If you pay 10000 EUR you should feel free to use GNU Parallel without citing. If you send a copy of your published article to tange@gnu.org, it will be mentioned in the release notes of next version of GNU Parallel. With \ **--max-line-length-allowed**\ GNU \ **parallel**\ will report the maximal size of the command line: .. code-block:: perl parallel --max-line-length-allowed Output (may vary on different systems): .. code-block:: perl 131071 \ **--number-of-cpus**\ and \ **--number-of-cores**\ run system specific code to determine the number of CPUs and CPU cores on the system. On unsupported platforms they will return 1: .. code-block:: perl parallel --number-of-cpus parallel --number-of-cores Output (may vary on different systems): .. code-block:: perl 4 64 ******** Profiles ******** The defaults for GNU \ **parallel**\ can be changed systemwide by putting the command line options in \ **/etc/parallel/config**\ . They can be changed for a user by putting them in \ **~/.parallel/config**\ . Profiles work the same way, but have to be referred to with \ **--profile**\ : .. code-block:: perl echo '--nice 17' > ~/.parallel/nicetimeout echo '--timeout 300%' >> ~/.parallel/nicetimeout parallel --profile nicetimeout echo ::: A B C Output: .. code-block:: perl A B C Profiles can be combined: .. code-block:: perl echo '-vv --dry-run' > ~/.parallel/dryverbose parallel --profile dryverbose --profile nicetimeout echo ::: A B C Output: .. code-block:: perl echo A echo B echo C *************** Spread the word *************** I hope you have learned something from this tutorial. If you like GNU \ **parallel**\ : - (Re-)walk through the tutorial if you have not done so in the past year (https://www.gnu.org/software/parallel/parallel_tutorial.html) - Give a demo at your local user group/your team/your colleagues - Post the intro videos and the tutorial on Reddit, Mastodon, Diaspora\*, forums, blogs, Identi.ca, Google+, Twitter, Facebook, Linkedin, and mailing lists - Request or write a review for your favourite blog or magazine (especially if you do something cool with GNU \ **parallel**\ ) - Invite me for your next conference If you use GNU \ **parallel**\ for research: - Please cite GNU \ **parallel**\ in you publications (use \ **--citation**\ ) If GNU \ **parallel**\ saves you money: - (Have your company) donate to FSF or become a member https://my.fsf.org/donate/ (C) 2013-2024 Ole Tange, GFDLv1.3+ (See LICENSES/GFDL-1.3-or-later.txt)