Execute Unix command in a Perl script

Question

How I can make the following external command within ticks work with variables instead?

Or something similar?

sed -i.bak -e '10,16d;17d' $docname; (this works)

I.e., sed -i.bak -e '$line_number,$line_end_number;$last_line' $docname;

Could try this: system(qq{sed -i.bak -e '$line_number,$line_end_number;$last_line' $docname}) — macduff
– macduff, Commented Mar 12, 2012 at 20:17

Jonathan Leffler · Accepted Answer · 2012-03-12 20:15:57Z

3

my $result = 
      qx/sed -i.bak -e "$line_number,${line_end_number}d;${last_line}d" $docname/;

Where the line split avoid the horizontal scroll-bar on SO; otherwise, it would be on one line.

Or, since it is not clear that there's any output to capture:

system "sed -i.back '$line_number,${line_end_number}d;${last_line}d' $docname";

Or you could split that up into arguments yourself:

system "sed", "-i.back", "$line_number,${line_end_number}d;${last_line}d", "$docname";

This tends to be safer since the shell doesn't get a chance to interfere with the interpretation of the arguments.

answered Mar 12, 2012 at 20:15

Jonathan Leffler

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1 Comment

Keith Thompson Over a year ago

I advise always using the multi-argument form of Perl's system() function, unless you have a specific requirement to have the shell parse some of the arguments (I/O redirection. etc.)

eeerahul · Accepted Answer · 2012-03-13 06:37:48Z

0

@args = ("command", "arg1", "arg2");
system(@args) == 0 or die "system @args failed: $?"

Furthermore on the manual:

perldoc -f system

edited Mar 13, 2012 at 6:37

eeerahul

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answered Mar 12, 2012 at 20:16

dominix

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Comments

Peter Mortensen · Accepted Answer · 2019-07-31 21:01:33Z

0

I think you should read up on using qq for strings.

You probably want something like this:

use strict;
use warnings;

my     $line_number = qq|10|;
my $line_end_number = qq|16d|;
my       $last_line = qq|17d|;
my        $doc_name = qq|somefile.bak|;
my     $sed_command = qq|sed -i.bak -e '$line_number,$line_end_number;$last_line' $doc_name;|;

print $sed_command;
qx|$sed_command|;

edited Jul 31, 2019 at 21:01

Peter Mortensen

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answered Mar 12, 2012 at 20:32

Craig Treptow

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