With Perl
perl -i -ne'next if /clean_history_in_os=true/ && ++$ok > 1; print' file
This increments the counter when on that line and if > 1
it skips the line, otherwise prints
The question came up of how to pass the pattern to Perl if we have it as a shell variable. Below I assume that the shell variable $VAR
contains the string clean_history...
In all this a shell variable’s value is directly used as a pattern in a regex. If it’s the literal string from the question then the code below goes as given. However, if there may be special characters they should be escaped; so you may want to precede the pattern with \Q
when used in regex. As a general note, one should take care to not use input from the shell to run code (say under /e
).
-
Pass it as an argument, which is then available in @ARGV
perl -i -ne' BEGIN { $qr=shift; }; next if /$qr/ && ++$ok > 1; print ' "$VAR" file
where the
BEGIN
block runs in theBEGIN
phase, before runtime (so not for the following iterations). In it shift removes the first element from@ARGV
, which in the above invocation is the value in$VAR
, first interpolated by shell. Then the filenamefile
remains in@ARGV
, so available for processing under-n
(file is opened and its lines iterated over) -
Use the
-s
switch, which enables command-line switches for the programperl -i -s -ne'next if /$qr/ && ++$ok > 1; print' -- -qr="$VAR" file
The
--
(after the one-line program under''
) marks the start of arguments for the program; then-qr
introduces a variable$qr
into the program, with a value assigned to it as above (with just-qr
the variable$qr
gets value1
, so is a flag).Any such options must come before possible filenames, and they are removed from
@ARGV
so the program can then normally process the submitted files. -
Export the bash variable, making it an environment variable which can then be accessed in the Perl program via
%ENV
hashexport VAR="clean_history..." perl -i -ne'next if /$ENV{VAR}/ && ++$ok > 1; print' file
or, if $VAR
is used only in this one-liner, can use the shorter (what must be on one line)
VAR="clean_history..." perl -i -ne'...' file
I would rather recommend either of the first two options, over this one.
These are ways to pass input to a Perl program entered entirely on the command-line (one-liner), without STDIN
or files. With a script better use a library, in the first place Getopt::Long.
A refinement of the question given in a comment specifies that if the phrase clean_...
starts with a #
then that line should be skipped altogether. It’s simplest to separately test for that
next if /#$qr/; next if /$qr/ && ++$ok > 1; print
or, relying on short-circuiting
next if /#$qr/ || (/$qr/ && ++$ok > 1); print
The first version is less error prone and probably clearer.