Question

Here is my scalar:

my $var = "foo1";

and here is what I tried to do:

$var =~ s/[0-9]/_[0-9]/;

Result:

foo_[0-9]

Expected Result:

foo_1

It would be great if you could answer for finding foo and adding the underscore after the match, and also finding 1 and adding the underscore before.

$var = s/foo/something/

and

$var = s/[0-9]/something/

Thanks in advance

Answer 1

Capture what you want to insert, then insert what you captured:

s/([0-9])/_$1/;

Or use a lookahead:

s/(?=[0-9])/_/;

As requested, solutions that also match foo:

s/(foo)([0-9])/$1_$2/;

s/foo\K([0-9])/_$1/;

s/foo\K(?=[0-9])/_/;

Note that captures slow down the match.