Perl regex. Why does this happen?

$h4X4_|=73}{ has asked for the wisdom of the Perl Monks concerning the following question:

I can not figure out why its output changes.

my $nothing = '';
my $list = <<LIST;
thing 1
thing 2 $nothing
thing  3
thing  4
LIST
$list =~ s/\s{2}/2/g;
print $list;
# output:
#thing 1
#thing 22thing23
#thing24
[download]

I would like the output.

thing 1
thing 2
thing23
thing24
[download]

Comment on Perl regex. Why does this happen? Select or Download Code

Replies are listed 'Best First'.
Re: Perl regex. Why does this happen? by hippo (Archbishop) on Jun 03, 2016 at 09:29 UTC
The problem is that `\s` matches any type of whitespace including the newline. If you change your regex line to be: `$list =~ s/ {2}/2/g;` [download] it should work as you intend.	[reply] [d/l] [select]
Re: Perl regex. Why does this happen? by BrowserUk (Patriarch) on Jun 03, 2016 at 09:32 UTC
Why does this happen? Because \s match all whitespace chars, including \n; thus \s{2} matches " \n" in your second line. Based on the data you've provided, `s[(\s{2})(?=\d)][2]g` should do what you want. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice. Not understood.	[reply] [d/l]
Re^2: Perl regex. Why does this happen? by OneTrueDabe (Acolyte) on Jun 07, 2016 at 01:29 UTC
Based on the data you've provided, `s[(\s{2})(?=\d)][2]g` should do what you want. Or (more simply, IMHO) use `\h` [horizontal whitespace] instead of `\s`	[reply] [d/l] [select]
Re^3: Perl regex. Why does this happen? by AnomalousMonk (Archbishop) on Jun 07, 2016 at 04:02 UTC
`\h` added with Perl version 5.10. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^4: Perl regex. Why does this happen? (^\S\n) by tye (Sage) on Jun 07, 2016 at 15:53 UTC
Re: Perl regex. Why does this happen? by Anonymous Monk on Jun 03, 2016 at 10:34 UTC
See how the regex engine does the matching with use re 'debug'; or in color with rxrx	[reply]