Re^3: regex to rename last

A couple of reasons. First, I can never remember the exact syntax of the look-around assertions, so I have to perldoc perlre each time I use one. This makes it advanced in my mind. I guess this is highly subjective, so your point is taken.

Second, the more features are used in a regular expression, the more there is to translate when you want to use it in another tool. Doing without look-ahead brings the RE to a lower common denominator, so to speak.

Comment on Re^3: regex to rename last _ with ,

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Re^4: regex to rename last _ with , by AppleFritter (Vicar) on Sep 14, 2014 at 14:57 UTC
First, I can never remember the exact syntax of the look-around assertions They're fairly mnemonic, actually: `(?=PATTERN)` - positive lookahead. Mnemonic: the following data equals (`=`; i.e. matches) the supplied pattern. `(?!PATTERN)` - negative lookahead. Mnemonic: the following data does not (`!`) match the pattern. `(?<=PATTERN)` - positive lookbehind. Mnemonic: the preceding (`<`) data equals (`=`; i.e. matches) the pattern. `(?<!PATTERN)` - negative lookbehind. Mnemonic: the preceding (`<`) data does not (`!`) match the pattern. Personally I might've chosen `(?>=PATTERN)` and `(?>!PATTERN)` for lookahead assertions to make the syntax of these symmetric in direction as well (though that would've clashed with non-backtracking patterns), but even this way I still think these are fairly easy to remember.	[reply]
Re^5: regex to rename last _ with , by Grimy (Pilgrim) on Sep 15, 2014 at 09:36 UTC
Look-ahead is used much more frequently than lookbehind, hence the shorter syntax. Perl is quite heavily Huffman coded. Look-behind is actually almost useless, since variable-length look-behind isn’t supported. It can be approximated using \K	[reply]