Re^4: getting answer 70 years off

Ah, if you write your regexes that way ( "qr{...}" ), then you wouldn't need to escape them, but when you use " /.../ " notation, they do have to be escaped, or else they end the regex. TMTOWTDI. Vim highlights both of these cases accurately in my limited testing.

$ perl -Mstrict -Mwarnings -e 'my $re = /[ /\\-]/'
Unmatched [ in regex; marked by <-- HERE in m/[ <-- HERE  / at -e line
+ 1.
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Re^5: getting answer 70 years off by kcott (Archbishop) on Jan 25, 2014 at 00:11 UTC
Yes, you're quite correct: when using '`/`' as a delimiter, you'll need to escape instances of that delimiter in the regex. I should've looked more closely at the delimiters you were using — my apologies. However, this is true for any delimiter. Here I needed to escape the '`-`' but not the '`/`' (with `m-...-`); with a delimiter not occurring in the regex (e.g. `m!...!`), no special escapes are required: `$ perl -Mstrict -Mwarnings -le 'my $x = "-"; print $x =~ m-[ /\\-]- ? +1 : 0' Unmatched [ in regex; marked by <-- HERE in m/[ <-- HERE /\\/ at -e l +ine 1. $ perl -Mstrict -Mwarnings -le 'my $x = "-"; print $x =~ m-[ /\\\-]- ? + 1 : 0' 1 $ perl -Mstrict -Mwarnings -le 'my $x = "-"; print $x =~ m![ /\\-]! ? +1 : 0' 1` [download] You may be interested in this (from "perlop: Regexp Quote-Like Operators"): "If "/" is the delimiter then the initial `m` is optional. With the `m` you can use any pair of non-whitespace (ASCII) characters as delimiters. This is particularly useful for matching path names that contain "/", to avoid LTS (leaning toothpick syndrome)." [my emphasis] -- Ken	[reply] [d/l] [select]

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Re^5: getting answer 70 years off
by kcott (Archbishop) on Jan 25, 2014 at 00:11 UTC

Yes, you're quite correct: when using '/' as a delimiter, you'll need to escape instances of that delimiter in the regex. I should've looked more closely at the delimiters you were using — my apologies.

However, this is true for any delimiter. Here I needed to escape the '-' but not the '/' (with m-...-); with a delimiter not occurring in the regex (e.g. m!...!), no special escapes are required:

$ perl -Mstrict -Mwarnings -le 'my $x = "-"; print $x =~ m-[ /\\-]- ? 
+1 : 0'
Unmatched [ in regex; marked by <-- HERE in m/[ <-- HERE  /\\/ at -e l
+ine 1.

$ perl -Mstrict -Mwarnings -le 'my $x = "-"; print $x =~ m-[ /\\\-]- ?
+ 1 : 0'
1

$ perl -Mstrict -Mwarnings -le 'my $x = "-"; print $x =~ m![ /\\-]! ? 
+1 : 0'
1
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You may be interested in this (from "perlop: Regexp Quote-Like Operators"):

"If "/" is the delimiter then the initial m is optional. With the m you can use any pair of non-whitespace (ASCII) characters as delimiters. This is particularly useful for matching path names that contain "/", to avoid LTS (leaning toothpick syndrome)." [my emphasis]

-- Ken

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