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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.


In reply to Re^4: regex to rename last _ with , by AppleFritter
in thread regex to rename last _ with , by Anonymous Monk

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