Regex - Should hyphens be escaped

Question

Possible Duplicate    How to match hyphens with Regular Expression        Hyphen is a special character in regex  for instance  to select a range  I could do something like     0-9A-F    But outside of square brackets it s just a regular character right  I ve tested this on a couple of online regex testers  and hyphens seem to function as a normal character outside of square brackets  or even inside of square brackets if it s not in-between two characters - eg  -g  seems to match - or g  whether it s escaped or not  I couldn t find the answer to this  but I m wondering whether or not it is conventional to escape hyphens   Thanks

User · Answer

Outside of character classes  it is conventional not to escape hyphens  If I saw an escaped hyphen outside of a character class  that would suggest to me that it was written by someone who was not very comfortable with regexes   Inside character classes  I don t think one way is conventional over the other  in my experience  it usually seems to be to put either first or last  as in  -     or     -   to avoid the backslash  but I ve also often seen it escaped instead  as in     -    and I wouldn t call that unconventional

User · Answer

Typically you would always put the hyphen first in the    match section   EG  to match any alphanumeric character including hyphens  written the long way   you would use  -a-zA-Z0-9

User · Answer

Correct on all fronts  Outside of a character class  that s what the  square brackets  are called  the hyphen has no special meaning  and within a character class  you can place a hyphen as the first or last character in the range  e g   -a-z  or  0-9-    OR escape it  e g   a-z -0-9   in order to add  hyphen  to your class   It s more common to find a hyphen placed first or last within a character class  but by no means will you be lynched by hordes of furious neckbeards for choosing to escape it instead    Actually    my experience has been that a lot of regex is employed by folks who don t fully grok the syntax  In these cases  you ll typically see everything escaped  e g   a-z           -     simply because the engineer doesn t know what s  special  and what s not    so they  play it safe  and obfuscate the expression with loads of excessive backslashes  You ll be doing yourself  your contemporaries  and your posterity a huge favor by taking the time to really understand regex syntax before using it    Great question

[regex] Regex - Should hyphens be escaped?

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