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We should double for a backslash escape a forward slash / in a regular expression. A backslash \ is used to denote character classes, e.g. \d . So it's a special character in regular expression (just like in regular strings).
/Delimiters/ Delimiters have an impact on escaping: if the delimiter is / and the regex needs to look for / literals, then the forward slash must be escaped before it can be a literal ( \/ ).
The forward slash character is used to denote the boundaries of the regular expression: ? /this_is_my_regular_expression/ The backslash character ( \ ) is the escaping character. It can be used to denote an escaped character, a string, literal, or one of the set of supported special characters.
The \ is known as the escape code, which restore the original literal meaning of the following character. Similarly, * , + , ? (occurrence indicators), ^ , $ (position anchors) have special meaning in regex. You need to use an escape code to match with these characters.
What context/language? Some languages use / as the pattern delimiter, so yes, you need to escape it, depending on which language/context. You escape it by putting a backward slash in front of it: \/ For some languages (like PHP) you can use other characters as the delimiter and therefore you don't need to escape it. But AFAIK in all languages, the only special significance the / has is it may be the designated pattern delimiter.
Here are a few options:
In Perl, you can choose alternate delimiters. You're not confined to m//. You could choose another, such as m{}. Then escaping isn't necessary. As a matter of fact, Damian Conway in "Perl Best Practices" asserts that m{} is the only alternate delimiter that ought to be used, and this is reinforced by Perl::Critic (on CPAN). While you can get away with using a variety of alternate delimiter characters, // and {} seem to be the clearest to decipher later on. However, if either of those choices result in too much escaping, choose whichever one lends itself best to legibility. Common examples are m(...), m[...], and m!...!.
In cases where you either cannot or prefer not to use alternate delimiters, you can escape the forward slashes with a backslash: m/\/[^/]+$/ for example (using an alternate delimiter that could become m{/[^/]+$}, which may read more clearly). Escaping the slash with a backslash is common enough to have earned a name and a wikipedia page: Leaning Toothpick Syndrome. In regular expressions where there's just a single instance, escaping a slash might not rise to the level of being considered a hindrance to legibility, but if it starts to get out of hand, and if your language permits alternate delimiters as Perl does, that would be the preferred solution.
Use the backslash \ or choose a different delimiter, ie m#.\d# instead of /.\d/
"In Perl, you can change the / regular expression delimiter to almost any other special character if you preceed it with the letter m (for match);"
If the delimiter is /, you will need to escape.
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