Perl regex replace?

Question

Why does this work:

$my_str=~s/://g;

But this does not:

$my_str=~s/:://g;

I have a string that looks something like this: ::this:is:my:string and I need to remove the :: but not touch the :.

It works for me. At least it does with a string that looks exactly like "::this:is:my:string". I have no idea what it will do with a string that looks "something like" that. If you want real answers, show real code. — Keith Thompson
– Keith Thompson, Commented Aug 29, 2011 at 15:15
Add use strict; use warnings; to the top of your script. If you can still run the script without warnings, post your code. — TLP
– TLP, Commented Aug 29, 2011 at 16:39
Oh you know what. This script was written by another guy in my department and he commented out use strict; and use warnings; This explains why I was so puzzled. Thanks! — djswartz
– djswartz, Commented Aug 29, 2011 at 18:34

fenceop · Accepted Answer · 2015-03-15 02:45:35Z

14

Works fine for me:

$ echo "::this:is:my:string" | perl -ne "s/:://g; print;"
this:is:my:string

edited Mar 15, 2015 at 2:45

fenceop

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answered Aug 29, 2011 at 15:14

Ken Simon

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Comments

Kevin · Accepted Answer · 2011-08-29 15:18:21Z

7

Are you sure you don't have any typos in your code? And that this substitution is in fact the problem? The following program worked for me:

my $var = '::a:b:c::';
print "$var\n";
$var =~ s/:://g;
print "$var\n";

Output:

$ perl test.pl
::a:b:c::
a:b:c
$

Edit to add a couple suggestions:

Print the variable immediately before and after the substitution.
No immediately the problem at hand, but if you only need to remove the :: at the beginning of the string, you may want to add a ^ to the regex to indicate that.

answered Aug 29, 2011 at 15:18

Kevin

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Comments

ikegami · Accepted Answer · 2011-08-29 19:00:17Z

3

There are two things I can think of that would cause $my_str =~ s/:://g; fail:

$my_str doesn't contains what you say it contains.
pos($my_str) is set.

To make sure $my_str contains what you think it does, you could use Data::Dumper, but make sure to do $Data::Dumper::Useqq = 1; before using Dumper.

But first, make sure you aren't doing something like

if ($my_str =~ /.../g) {
   ...
   $my_str =~ s/:://g;
   ...
}

if ($my_str =~ /.../g) is a common mistake, and it could cause this problem. (I don't know why since it doesn't even make sense conceptually.) If so, get rid of the g in the if condition.

edited Aug 29, 2011 at 19:00

answered Aug 29, 2011 at 18:54

ikegami

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