Perl regex replace?

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开发者_开发知识库 :.

Works fine for me:

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

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:

1. Print the variable immediately before and after the substitution.
2. 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.

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

1. $my_str doesn't contains what you say it contains.
2. pos($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.