elements not reversing inside a map

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

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Re: elements not reversing inside a map by merlyn (Sage) on May 05, 2005 at 20:07 UTC
reverse in a list context is a list reverse. If you want a string reverse, you have to have a scalar context. Try adding "scalar" in front of your first "reverse". -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^2: elements not reversing inside a map by Transient (Hermit) on May 05, 2005 at 20:35 UTC
Ok, I had overlooked that map evaluated $_ in a list context. My question below stil stands, however. Why does (reverse $_)\|\|"" work?	[reply]
Re^3: elements not reversing inside a map by merlyn (Sage) on May 05, 2005 at 21:01 UTC
Because it puts it into scalar context? -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^4: elements not reversing inside a map by Transient (Hermit) on May 05, 2005 at 21:32 UTC
Re^5: elements not reversing inside a map by chromatic (Archbishop) on May 05, 2005 at 21:48 UTC
Re: elements not reversing inside a map by Roy Johnson (Monsignor) on May 05, 2005 at 20:18 UTC
And then to finally get "filename:ext", you'll need yet another reverse: `perl -le '$,=":";print reverse map scalar(reverse), split( /\./, (rev +erse "filename.ext"), 2)'` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re: elements not reversing inside a map by salva (Canon) on May 05, 2005 at 20:11 UTC
the `reverse` call inside `map` is called in list context so it reverses the list formed by its arguments `($_)`. Call it inside `scalar` to obtain the desired behavior: `perl -le '$,=":";print map {scalar(reverse $_)} split( /\./, (reverse +"filename.ext"), 2)'` [download]	[reply] [d/l] [select]
Re: elements not reversing inside a map by Zaxo (Archbishop) on May 05, 2005 at 20:17 UTC
The scalar reversal to string order is occuring in the string you split, try this: `perl -le '$,=":";print split( /\./, "filename.ext", 2)'` I'm not sure why you had all those reverse operators in there. Would `s/\./:/` have sufficed? After Compline, Zaxo	[reply] [d/l] [select]
Re: elements not reversing inside a map by Codon (Friar) on May 05, 2005 at 21:02 UTC
You are doing a 'reverse "filename.ext"' which reverses the string into "txe.emanelif". You want to perhaps do this: `> perl -le '$,=":";print reverse split /\./, "filename.ext", 2' ext:filename` [download] Edit: I realize that you are actually wanting to split on the last 'dot' to get the extension; that's why you did the string reverse. Here's a better way: `perl -le '$,=":";print reverse( "filename.ext" =~ /(.*)\.([^.]+)$/ )'` [download] Enjoy! Ivan Heffner Sr. Software Engineer, DAS Lead WhitePages.com, Inc.	[reply] [d/l] [select]
Re^2: elements not reversing inside a map by Transient (Hermit) on May 05, 2005 at 21:29 UTC
Unfortunately, that will not do what I want when the filename contains a '.' `perl -le '$,=":";print reverse split /\./, "filename.200505.ext", 2' >200505.ext:filename` [download] when I would want (unbeknownst to all) ext:filename.200505	[reply] [d/l]
Re^3: elements not reversing inside a map by eibwen (Friar) on May 06, 2005 at 00:11 UTC
To parse the file extension, just capture the text following the last `.`: `$filename =~ /(?<=\.)([^.]+)$/;`	[reply] [d/l] [select]
Re: elements not reversing inside a map by Transient (Hermit) on May 05, 2005 at 20:10 UTC
Hmm... changing this to either `perl -le '$,=":";print map {$_=reverse $_} split( /\./, (reverse "file +name.ext"), 2)'` [download] or `perl -le '$,=":";print map {(reverse $_)\|\|""} split( /\./, (reverse "f +ilename.ext"), 2)'` [download] works... the statement I was working on prior to my posting of the question here was similar to the latter statement, which threw me off. Does \|\| evaluate into $_?	[reply] [d/l] [select]
Re: elements not reversing inside a map by ikegami (Patriarch) on May 05, 2005 at 20:25 UTC
Roy Johnson has a working solution. The following will also do the trick: `perl -le '$_="filename.ext"; s/^(.)\.([^.])$/$2:$1/; print($_);'` [download] Both Roy's and mine splits at the last ".", just like you were trying to do. By the way, I would further postulate that extentions don't have spaces in them: `perl -le '$_="filename.ext"; s/^(.)\.([^.\s])$/$2:$1/; print($_);'` [download]	[reply] [d/l] [select]