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]