Using variable in substitute regex producing odd results

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

Mindful Monks,

this code snippet:

$delimiter = "|";
$line = "|45.55.186.846|asdf|24_12:20:19|ab|2004|18467|409|19|us|22348
+|i|cnor|f|55p|2";
$line =~ s/$delimiter/\,/g;
print "$line\n";
[download]

produces the output:

,|,4,5,.,5,5,.,1,8,6,.,8,4,6,|,a,s,d,f,|,2,4,_,1,2,:,2,0,:,1,9,|,a,b,|,2,0,0,4,|,1,8,4,6,7,|,4,0,9,|,1,9,|,u,s,|,2,2,3,4,8,|,i,|,c,n,o,r,|,f,|,5,5,p,|,2,

whereas I was looking for:

,45.55.186.846,asdf,24_12:20:19,ab,2004,18467,409,19,us,22348,i,cnor,f,55p,2

Something obvious undoubtedly.
Thanks.

Forget that fear of gravity,
Get a little savagery in your life.

Comment on Using variable in substitute regex producing odd results Download Code

Replies are listed 'Best First'.
Re: Using variable in substitute regex producing odd results by Errto (Vicar) on Sep 06, 2005 at 23:26 UTC
The pipe character "\|" is a regex metacharacter, so your regex becomes "match nothing or nothing" which, with the /g modifier, is effectively equivalent to matching at the boundary between every adjoining character in your string. The generic solution for this is to escape the string within the regexp: `$line =~ s/\Q$delimeter\E/,/g;` [download]	[reply] [d/l]
Re: Using variable in substitute regex producing odd results by GrandFather (Saint) on Sep 06, 2005 at 23:26 UTC
You need to quote your string with \Q\E because it contains \| which in a regex means `or`. What you want is: `$line =~ s/\Q$delimiter\E/\,/g;` [download] Note that your original code acted as a "match anything" so it interspersed a comma between each character in the target string. Perl is Huffman encoded by design.	[reply] [d/l] [select]
Re: Using variable in substitute regex producing odd results by sh1tn (Priest) on Sep 06, 2005 at 23:28 UTC
You may want to look at `\Q \E` operators: `... $line =~ s/\Q$delimiter/\,/g; ...` [download]	[reply] [d/l] [select]
Re: Using variable in substitute regex producing odd results by punch_card_don (Curate) on Sep 06, 2005 at 23:32 UTC
Yep, that did it - thanks all. Forget that fear of gravity, Get a little savagery in your life.	[reply]