regex help needed

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

I'm trying to match an instance of a string but only the last instance if it exists. Here is my code:

use strict;
use warnings;

my $string = some data, echo DONE Upgrading packages...  Cleaning upgr
+ade files...  Starting services... DONE';

if ($string =~ /(?!echo Done) Done/i) {
    print "match found\n";
}
[download]

The problem is that if the last DONE doesn't exist then a match is still seen and I need to exclude the 'echo DONE'. I suppose I could always remove any instance of 'echo DONE' and then try my match...but I was hoping to do it in my regex.

Thanks

Comment on regex help needed Download Code

Replies are listed 'Best First'.
Re: regex help needed by kennethk (Abbot) on Jul 17, 2009 at 16:45 UTC
Two quick possibilities come to mind, based upon your provided input: Since 'DONE' is the last element of your string, you could anchor to the end of the string with ^ (Regular Expressions), a la: `$string =~ /DONE$/i;` If you know the only undesirable DONE follows echo and will be the only one that follows echo, you could use a negative look behind assertion (Looking ahead and looking behind) to skip that case: `$string =~ /(?<!echo\s)DONE/i;`	[reply] [d/l] [select]
Re^2: regex help needed by Anonymous Monk on Jul 17, 2009 at 16:56 UTC
using the negative look behind worked...thanks!	[reply]
Re: regex help needed by jwkrahn (Abbot) on Jul 17, 2009 at 16:40 UTC
It looks like you want something like: `if ($string =~ /(?<!echo )Done$/i) { # update to look-behind instead o +f look-ahead print "match found\n"; }` [download]	[reply] [d/l]
Re^2: regex help needed by Anonymous Monk on Jul 17, 2009 at 16:47 UTC
Thats better but DONE isn't always the last item in the string.	[reply]
Re^2: regex help needed by JavaFan (Canon) on Jul 17, 2009 at 16:51 UTC
That's not any different from `/Done$/`. (Originally jwkrahn had `/(?!echo )done$/` - but he updated it after I posted my reply)	[reply] [d/l] [select]
Re: regex help needed by JavaFan (Canon) on Jul 17, 2009 at 17:07 UTC
A way using negative lookbehind as been shown. Others are: `/(?:^.{0,4}\|[^e].{4}\|[^c].{3}\|[^h].{2}\|[^o].\|[^ ])done/is /(.....)done(??{$1 eq "echo " ? "(FAIL)" : ""})\|^.{0,4}done/is # Repl +ace (FAIL) with (?!) pre-5.10` [download] Of course, if you know you only need to look at DONE at the end, you can use: `!/echo done$/i && /done$/i` [download]	[reply] [d/l] [select]