Re^2: regex question

The problem with the approach you advocate here is that look-behind assertions are fixed width so you can't do something like (?<=\d+\s). If you declare the string like this

my $str="1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
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how do you replace the 12th field?

I'm all for look-around assertions but I don't think they are suited to this particular problem.

Cheers,

JohnGG

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Re^3: regex question by convenientstore (Pilgrim) on Nov 12, 2007 at 15:55 UTC
I thought of look behind but decide against it since field 9 can and will have dynamic variables.. still working on this.	[reply]
Re^4: regex question by convenientstore (Pilgrim) on Nov 12, 2007 at 17:06 UTC
if you capture something by () in regex and you get $1,$2,$3 and so on, why can't you just do `s/$2/something/` [download] In this script, it's doing it but it's changing the value rather than position. What i mean is, `[root@myserver tmp]# cat perl.test #!/usr/bin/perl -w use strict; my $string = "123 123 345"; if ("$string" =~ /(\d+)\s+(\d+)\s+(\d+)/) { $string =~ s/$2/something/; print "$string\n"; } [root@myserver tmp]# ./!$ ./perl.test something 123 345` [download] I wanted this to change the value of position $2, Therefore wanted to see 123 something 345	[reply] [d/l] [select]
Re^5: regex question by johngg (Canon) on Nov 12, 2007 at 19:21 UTC
That happens because your second capture, held in `$2`, is "123" so in your substitution inside the `if` `$2` is interpolated to give `s/123/something/`, which runs quite happily and replaces the first occurence of "123" in `$string`. Had your string been "987 123 345" your code would have given the result you wanted but only as a side effect of your error. You could do it like this (not tested) `use strict; use warnings; my $string = q{123 123 345}; if ( $string =~ s{^(\d+\s+)(?:\d+)(\s+\d+)}{$1something$2} ) { print qq{Succeeded\n$string\n}; } else { print qq{Failed\n$string\n}; }` [download] I hope this makes things a bit clearer. Cheers, JohnGG	[reply] [d/l] [select]