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2.2 Command-Line Options

The full format for invoking sed is:


sed may be invoked with the following command-line options:


Print out the version of sed that is being run and a copyright notice, then exit.


Print a usage message briefly summarizing these command-line options and the bug-reporting address, then exit.


By default, sed prints out the pattern space at the end of each cycle through the script (see How sed works). These options disable this automatic printing, and sed only produces output when explicitly told to via the p command.


Print the input sed program in canonical form, and annotate program execution.

$ echo 1 | sed '\%1%s21232'

$ echo 1 | sed --debug '\%1%s21232'
  /1/ s/1/3/
INPUT:   'STDIN' line 1
COMMAND: /1/ s/1/3/
-e script

Add the commands in script to the set of commands to be run while processing the input.

-f script-file

Add the commands contained in the file script-file to the set of commands to be run while processing the input.


This option specifies that files are to be edited in-place. GNU sed does this by creating a temporary file and sending output to this file rather than to the standard output.1.

This option implies -s.

When the end of the file is reached, the temporary file is renamed to the output file’s original name. The extension, if supplied, is used to modify the name of the old file before renaming the temporary file, thereby making a backup copy2).

This rule is followed: if the extension doesn’t contain a *, then it is appended to the end of the current filename as a suffix; if the extension does contain one or more * characters, then each asterisk is replaced with the current filename. This allows you to add a prefix to the backup file, instead of (or in addition to) a suffix, or even to place backup copies of the original files into another directory (provided the directory already exists).

If no extension is supplied, the original file is overwritten without making a backup.

Because -i takes an optional argument, it should not be followed by other short options:

sed -Ei '...' FILE

Same as -E -i with no backup suffix - FILE will be edited in-place without creating a backup.

sed -iE '...' FILE

This is equivalent to --in-place=E, creating FILEE as backup of FILE

Be cautious of using -n with -i: the former disables automatic printing of lines and the latter changes the file in-place without a backup. Used carelessly (and without an explicit p command), the output file will be empty:

# WRONG USAGE: 'FILE' will be truncated.
sed -ni 's/foo/bar/' FILE
-l N

Specify the default line-wrap length for the l command. A length of 0 (zero) means to never wrap long lines. If not specified, it is taken to be 70.


GNU sed includes several extensions to POSIX sed. In order to simplify writing portable scripts, this option disables all the extensions that this manual documents, including additional commands. Most of the extensions accept sed programs that are outside the syntax mandated by POSIX, but some of them (such as the behavior of the N command described in Reporting Bugs) actually violate the standard. If you want to disable only the latter kind of extension, you can set the POSIXLY_CORRECT variable to a non-empty value.


This option is available on every platform, but is only effective where the operating system makes a distinction between text files and binary files. When such a distinction is made—as is the case for MS-DOS, Windows, Cygwin—text files are composed of lines separated by a carriage return and a line feed character, and sed does not see the ending CR. When this option is specified, sed will open input files in binary mode, thus not requesting this special processing and considering lines to end at a line feed.


This option is available only on platforms that support symbolic links and has an effect only if option -i is specified. In this case, if the file that is specified on the command line is a symbolic link, sed will follow the link and edit the ultimate destination of the link. The default behavior is to break the symbolic link, so that the link destination will not be modified.


Use extended regular expressions rather than basic regular expressions. Extended regexps are those that egrep accepts; they can be clearer because they usually have fewer backslashes. Historically this was a GNU extension, but the -E extension has since been added to the POSIX standard (, so use -E for portability. GNU sed has accepted -E as an undocumented option for years, and *BSD seds have accepted -E for years as well, but scripts that use -E might not port to other older systems. See Extended regular expressions.


By default, sed will consider the files specified on the command line as a single continuous long stream. This GNU sed extension allows the user to consider them as separate files: range addresses (such as ‘/abc/,/def/’) are not allowed to span several files, line numbers are relative to the start of each file, $ refers to the last line of each file, and files invoked from the R commands are rewound at the start of each file.


In sandbox mode, e/w/r commands are rejected - programs containing them will be aborted without being run. Sandbox mode ensures sed operates only on the input files designated on the command line, and cannot run external programs.


Buffer both input and output as minimally as practical. (This is particularly useful if the input is coming from the likes of ‘tail -f’, and you wish to see the transformed output as soon as possible.)


Treat the input as a set of lines, each terminated by a zero byte (the ASCII ‘NUL’ character) instead of a newline. This option can be used with commands like ‘sort -z’ and ‘find -print0’ to process arbitrary file names.

If no -e, -f, --expression, or --file options are given on the command-line, then the first non-option argument on the command line is taken to be the script to be executed.

If any command-line parameters remain after processing the above, these parameters are interpreted as the names of input files to be processed. A file name of ‘-’ refers to the standard input stream. The standard input will be processed if no file names are specified.



This applies to commands such as =, a, c, i, l, p. You can still write to the standard output by using the w or W commands together with the /dev/stdout special file


Note that GNU sed creates the backup file whether or not any output is actually changed.

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