How to match a ;

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

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Re: How to match a ; by GrandFather (Saint) on Feb 08, 2009 at 08:45 UTC
That matches strings where the only character on the line is a ';'. To match just the first character where you don't care what follows, omit the $. Perl's payment curve coincides with its learning curve.	[reply]
Re^2: How to match a ; by AnomalousMonk (Archbishop) on Feb 08, 2009 at 09:57 UTC
The regex of the OP will evaluate true for all strings except a string consisting of a single `';'` character optionally followed by a newline because `$line !~ m{^;$}` uses the `!~` negating binding operator. Update: corrected per GrandFather's reply below.	[reply] [d/l] [select]
Re^3: How to match a ; by GrandFather (Saint) on Feb 08, 2009 at 10:02 UTC
Argh! Quite right. It must be the heat here! Well, any string except one containing a single ';' optionally followed by a \n. Perl's payment curve coincides with its learning curve.	[reply]
Re: How to match a ; by ELISHEVA (Prior) on Feb 08, 2009 at 08:52 UTC
You also need to make sure that `$line` is clean of final ~~new lines~~ whitespace, otherwise your regex won't match your line because `$line` will end in ~~a new line~~ whitespace instead of ';' - see http://perldoc.perl.org/functions/chomp.html. Also you might consider `/^;\s$/` to strip trailing whitespace. Syntax wise, your regex is fine. Best, beth Update:*Correction (see jwkrahn and Grandfather below).	[reply] [d/l] [select]
Re^2: How to match a ; by GrandFather (Saint) on Feb 08, 2009 at 09:06 UTC
Actually no. $ matches an end of line, which may be a \n character. Consider: `my $line = ";\n"; print $line =~ /$_/ ? "" : "no ", "match: $_\n" for '^;$', '^;', "^;\\ +z";` [download] Prints: `match: ^;$ match: ^; no match: ^;\z` [download] Note that \z matches the physical end of the string. Perl's payment curve coincides with its learning curve.	[reply] [d/l] [select]
Re^3: How to match a ; by AnomalousMonk (Archbishop) on Feb 08, 2009 at 10:20 UTC
The `$` regex metacharacter will "[m]atch the end of the line (or before newline at the end)" (emphasis added, perlre section Regular Expressions). In the presence of the /m regex modifier, the behavior of `$` is enhanced.	[reply] [d/l] [select]
Re^3: How to match a ; by ELISHEVA (Prior) on Feb 08, 2009 at 10:29 UTC
I stand corrected, but it was actually '.' and '$' new line behavior I was confusing. I once spent a great deal of time beating my brains out until I figured out that '.' doesn't match `\n` unless you use the 's' modifier, e.g. `/;./s`. But the more I think about it, I also am finding '$' less clearer than I thought, but I'll save those questions for another thread. Best, beth Update 2: removed update 1, appears I still have '$' questions and will need to go to SOPW	[reply] [d/l] [select]
Re^3: How to match a ; by johngg (Canon) on Feb 08, 2009 at 23:13 UTC
I'm puzzled as to why you switched to double quotes and then had to escape the backslash in your third pattern. Sticking to single quotes or using `qw{ ... }` would have obviated that need. `$ perl -le ' > $line = qq{;\n}; > print > $line =~ m{$_} > ? q{} > : q{no }, > qq{match $_} > for q{^;$}, q{^;}, q{^;\z};' match ^;$ match ^; no match ^;\z $ perl -le ' $line = qq{;\n}; print $line =~ m{$_} ? q{} : q{no }, qq{match $_} for qw{ ^;$ ^; ^;\z };' match ^;$ match ^; no match ^;\z $` [download] Cheers, JohnGG	[reply] [d/l] [select]
Re^4: How to match a ; by GrandFather (Saint) on Feb 09, 2009 at 00:41 UTC
Re^2: How to match a ; by jwkrahn (Abbot) on Feb 08, 2009 at 08:58 UTC
The `$` anchor will match the end of the line with or without a newline at the end so `/^;$/` will match both `";"` and `";\n"`.	[reply] [d/l] [select]