sed isn't working within a perl script

nvivek has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks, I want to replace a particular content in my file with some pattern. I planned to use sed with -i option to replace the pattern and make the changes effect in a original file. My sample file content ( test.txt ) : 1 2 3 4 My script is as follows:

use strict;
use warnings;
system("sed -ie 's/\(.*\)/Number => \1/' test.txt");
[download]

When I executed the script, numerals aren't changed to Number => 1. It remains same. Note: When I executed the sed command in shell prompt, it replaced the content of file properly as Number => 1 properly.

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Re: sed isn't working within a perl script by Corion (Patriarch) on Oct 19, 2012 at 09:05 UTC
You will need to modify your string and properly quote the backslash so that it gets passed correctly to the shell. I recommend the following approach: `use strict; use warnings; my $cmd = "sed -ie 's/$.*$/Number => \1/' test.txt"; print "Launching [$cmd]\n"; system($cmd) == 0 or die "Couldn't launch [$cmd]: $! / $?";` [download] You will see that your single backslashes did not get passed through to the `sed` command. You will need to double them.	[reply] [d/l] [select]
Re^2: sed isn't working within a perl script by nvivek (Vicar) on Oct 19, 2012 at 10:39 UTC
You're right. Thank you so much. I just doubled the backslashes used in grouping and referring grouped pattern. Then it worked properly. I got confused because I didn't get any error while executing that code.	[reply]
Re^2: sed isn't working within a perl script by McA (Priest) on Oct 19, 2012 at 09:19 UTC
Hi, is it possible that a backslash gets lost in your solution or simply when posting your solution? I can't see a difference. Best regards McA	[reply]
Re^3: sed isn't working within a perl script by Corion (Patriarch) on Oct 19, 2012 at 09:20 UTC
I did only add the debugging help, not a solution to the problem itself.	[reply]
Re^4: sed isn't working within a perl script by McA (Priest) on Oct 19, 2012 at 09:28 UTC
Re^3: sed isn't working within a perl script by Anonymous Monk on Oct 19, 2012 at 09:21 UTC
corion posted the original with error checking, so the OP can see/understand what went wrong (how to debug, error check) and instructions on how to fix the problem (something for the OP to type)	[reply]
Re: sed isn't working within a perl script by Anonymous Monk on Oct 19, 2012 at 09:17 UTC
:D Calling sed from perl is like driving a bicycle inside a car -- just drive the car The perl oneliner equivalent (as s2p helps me understand it) `perl -i -l -p -e ' s /(.)/Number => ${1}/s; ' test.txt` [download] But you still don't want to use system to run that oneliner instead use `use File::Slurp qw/ edit_file /; edit_file { s /(.)/Number => ${1}/s; } 'test.txt';` [download] or some such	[reply] [d/l] [select]
Re^2: sed isn't working within a perl script by Anonymous Monk on Oct 19, 2012 at 09:42 UTC
You want edit_file_lines because edit_file reads the whole file and not line-by-line	[reply]
Re^2: sed isn't working within a perl script by nvivek (Vicar) on Oct 19, 2012 at 10:37 UTC
I don't want to include new module to do this stuff. That's why, I preferred system function with sed command. Reason is I am going to add this stuff in 1000 lines of code which does other operation.	[reply]
Re^3: sed isn't working within a perl script by Anonymous Monk on Oct 19, 2012 at 11:48 UTC
I don't want to include new module to do this stuff. Reason is I am going to add this stuff in 1000 lines of code which does other operation. :) Like they say, do what makes sense to you But you might be interested in these other viewpoints :) You could always use open/readline ... see Re: modifying a file with regex! Or the instant classics on the subject of wheels :) Yes, even you can use CPAN Top 11 (GOOD) reasons not to use someone else's Modules, Top Seven (Bad) Reasons Not To Use Modules	[reply]
Re: sed isn't working within a perl script by aitap (Curate) on Oct 19, 2012 at 12:08 UTC
`system("sed -ie 's/$.$/Number => \1/' test.txt");` See the difference: `say "sed -ie 's/$.$/Number => \1/' test.txt"; say qq{sed -ie 's/$.$/Number => \1/' test.txt}; say q{sed -ie 's/$.$/Number => \1/' test.txt}; __END__ sed -ie 's/(.)/Number => /' test.txt sed -ie 's/(.)/Number => /' test.txt sed -ie 's/$.*$/Number => \1/' test.txt` [download] Double quotes do interpolate your backslashes, and they are lost when you run the command. You need a non-interpolating quote operator instead to pass your string unchanded to the shell. And I strongly advice you to use native Perl code instead, too. Sorry if my advice was wrong.	[reply] [d/l] [select]

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