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14.3.6 Miscellaneous Commands

There are a few more commands that do not fit into the previous categories, as follows:

dump [filename]

Dump byte code of the program to standard output or to the file named in filename. This prints a representation of the internal instructions that gawk executes to implement the awk commands in a program. This can be very enlightening, as the following partial dump of Davide Brini’s obfuscated code (see Signature Program) demonstrates:

gawk> dump
-|        # BEGIN
-|
-| [  1:0xfcd340] Op_rule           : [in_rule = BEGIN] [source_file = brini.awk]
-| [  1:0xfcc240] Op_push_i         : "~" [MALLOC|STRING|STRCUR]
-| [  1:0xfcc2a0] Op_push_i         : "~" [MALLOC|STRING|STRCUR]
-| [  1:0xfcc280] Op_match          :
-| [  1:0xfcc1e0] Op_store_var      : O
-| [  1:0xfcc2e0] Op_push_i         : "==" [MALLOC|STRING|STRCUR]
-| [  1:0xfcc340] Op_push_i         : "==" [MALLOC|STRING|STRCUR]
-| [  1:0xfcc320] Op_equal          :
-| [  1:0xfcc200] Op_store_var      : o
-| [  1:0xfcc380] Op_push           : o
-| [  1:0xfcc360] Op_plus_i         : 0 [MALLOC|NUMCUR|NUMBER]
-| [  1:0xfcc220] Op_push_lhs       : o [do_reference = true]
-| [  1:0xfcc300] Op_assign_plus    :
-| [   :0xfcc2c0] Op_pop            :
-| [  1:0xfcc400] Op_push           : O
-| [  1:0xfcc420] Op_push_i         : "" [MALLOC|STRING|STRCUR]
-| [   :0xfcc4a0] Op_no_op          :
-| [  1:0xfcc480] Op_push           : O
-| [   :0xfcc4c0] Op_concat         : [expr_count = 3] [concat_flag = 0]
-| [  1:0xfcc3c0] Op_store_var      : x
-| [  1:0xfcc440] Op_push_lhs       : X [do_reference = true]
-| [  1:0xfcc3a0] Op_postincrement  :
-| [  1:0xfcc4e0] Op_push           : x
-| [  1:0xfcc540] Op_push           : o
-| [  1:0xfcc500] Op_plus           :
-| [  1:0xfcc580] Op_push           : o
-| [  1:0xfcc560] Op_plus           :
-| [  1:0xfcc460] Op_leq            :
-| [   :0xfcc5c0] Op_jmp_false      : [target_jmp = 0xfcc5e0]
-| [  1:0xfcc600] Op_push_i         : "%c" [MALLOC|STRING|STRCUR]
-| [   :0xfcc660] Op_no_op          :
-| [  1:0xfcc520] Op_assign_concat  : c
-| [   :0xfcc620] Op_jmp            : [target_jmp = 0xfcc440]
-|
…
-|
-| [     2:0xfcc5a0] Op_K_printf         : [expr_count = 17] [redir_type = ""]
-| [      :0xfcc140] Op_no_op            :
-| [      :0xfcc1c0] Op_atexit           :
-| [      :0xfcc640] Op_stop             :
-| [      :0xfcc180] Op_no_op            :
-| [      :0xfcd150] Op_after_beginfile  :
-| [      :0xfcc160] Op_no_op            :
-| [      :0xfcc1a0] Op_after_endfile    :
gawk>
help
h

Print a list of all of the gawk debugger commands with a short summary of their usage. ‘help command’ prints the information about the command command.

list [- | + | n | filename:n | nm | function]
l [- | + | n | filename:n | nm | function]

Print the specified lines (default 15) from the current source file or the file named filename. The possible arguments to list are as follows:

- (Minus)

Print lines before the lines last printed.

+

Print lines after the lines last printed. list without any argument does the same thing.

n

Print lines centered around line number n.

nm

Print lines from n to m.

filename:n

Print lines centered around line number n in source file filename. This command may change the current source file.

function

Print lines centered around the beginning of the function function. This command may change the current source file.

quit
q

Exit the debugger. Debugging is great fun, but sometimes we all have to tend to other obligations in life, and sometimes we find the bug and are free to go on to the next one! As we saw earlier, if you are running a program, the debugger warns you when you type ‘q’ or ‘quit’, to make sure you really want to quit.

trace [on | off]

Turn on or off continuous printing of the instructions that are about to be executed, along with the awk lines they implement. The default is off.

It is to be hoped that most of the “opcodes” in these instructions are fairly self-explanatory, and using stepi and nexti while trace is on will make them into familiar friends.


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