Replace all occurrences but the last

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

Hi monks,

I'm trying to have a regex to change the filenames on the left to the ones on the right:

1) mypic.jpg.jpg => mypic_jpg.jpg
2) mypic.jpg.jpg.jpg => mypic_jpg_jpg.jpg
2) fish.fish.gif => fish_fish.gif

Basically, I want to replace every dot but the last with an underscore.

I haven't had much luck yet so I don't have any code to show.

Could someone enlighten me?

Thanks in anticipation :)

Update: Thanks to all for your help :)

Comment on Replace all occurrences but the last

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•Re: Replace all occurrences but the last by merlyn (Sage) on Aug 22, 2004 at 15:24 UTC
untested: `s/\.(?=.*?\.)/_/g;` [download] -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l]
Re^2: Replace all occurrences but the last by kiat (Vicar) on Aug 22, 2004 at 15:27 UTC
Thanks, merlyn! I was trying with the positive lookahead thing but I just didn't get it.	[reply]
Re: Replace all occurrences but the last by ysth (Canon) on Aug 22, 2004 at 15:51 UTC
`substr($s, 0, rindex($s, ".")) =~ y/./_/;` [download]	[reply] [d/l]
Re: Replace all occurrences but the last by Aristotle (Chancellor) on Aug 22, 2004 at 18:35 UTC
`1 while s/ \. ( .* \. ) /_$1/x;` [download] You can also make that non-greedy, it doesn't matter. Makeshifts last the longest.	[reply] [d/l]
Re: Replace all occurrences but the last by ambrus (Abbot) on Aug 22, 2004 at 15:31 UTC
One solution is to split the string at the last dot, then change the dots to underscores everywhere before it. `$_ = "mypic.jpg.jpg"; if (/^(.)(\..)/s) { my($p, $s) = ($1, $2); $p=~y/./_/; $_ = $p.$s; } print $_, $/;` [download] The if is needed so that you don't get an error if the string does not have a dot in it. Update: Ysth's reply has reminded me that you can bind substitutions to substr. That's indeed a simpler solution than what I've given above. Thus, here's a new variant using the same feature: `$_ = "mypic.jpg.jpg"; /^(.)\./s and substr($_, 0, $+[1])=~s/\./_/g; print $_, $/;` [download] Update 2:* Added hat anchor before `(.)`. Is that good? Update 3:* I mean Why does a Perl 5.6 regex run a lot slower on Perl 5.8?	[reply] [d/l] [select]
Re: Replace all occurrences but the last by ambrus (Abbot) on Aug 22, 2004 at 16:31 UTC
And now let's see a bit more trickier solution. `$_ = "fish.fish.gif"; s/\./\.\./g; s/^(.*)\./$1/s; s/\.\./_/g; print $_, $/;` [download]	[reply] [d/l]
Re: Replace all occurrences but the last by Anonymous Monk on Aug 23, 2004 at 11:03 UTC
`join _=>split/[.]/=>$_,y[.]__;` [download]	[reply] [d/l]
Re^2: Replace all occurrences but the last by Aristotle (Chancellor) on Aug 23, 2004 at 11:08 UTC
Silly rabbit. `:-)` Nice approach, though. `# legible: join( "_", split( /\./, $_, y/.// ) );` [download] The `tr///` here counts the dots in the string and uses the number as a limit to split — since the number is one less than the number of fragments delimited by dots, the last dot in the string does not get to serve as a delimiter. Makeshifts last the longest.	[reply] [d/l]