CODEWITHSUNDEEP
regexperl
ContraViZe
ContraViZe

Reputation: 121

Which characters must be escaped in a Perl regex pattern

Im trying to find files that are looking like this:

access_log-20160101
access_log-20160304
...

with perl regex i came up with something like this:

/^access_log-\d{8}$/

But im not sure about the "_" and the "-". are these metacharacter? What is the expression for this?

i read that "_" in regex is something like \w, but how do i use them in my exypression?

/^access\wlog-\d{8}$/ ?

Upvotes: 1

Views: 984

Answers (2)

Oleg V. Volkov
Oleg V. Volkov

Reputation: 22421

Underscore (_) is not a metacharacter and does not need to be quoted (though it won't change anything if you quote it).

Hyphen (-) IS a metacharacter that defines the range between two symbols inside a bracketed character class. However, in this particular position, it will be interpreted verbatim and doesn't need quoting since it is not inside [] with a symbol on both sides.

You can use your regexp as is; hyphens (-) might need quoting if your format changes in future.

Upvotes: 3

Borodin
Borodin

Reputation: 126722

Your regex pattern is exactly right

Neither underscore _ nor hyphen - need to be escaped. Outside a square-bracketed character class, the twelve Perl regex metacharacters are

  • Brackets ( ) [ {
  • Quantifiers * + ?
  • Anchors ^ $
  • Alternator |
  • Wild character .
  • The escape itself \

and only these must be escaped

If the pattern of your file names doesn't vary from what you have shown then the pattern that you are using

^access_log-\d{8}$

is correct, unless you need to validate the date string


Within a character class like [A-F] you must escape the hyphen if you want it to be interpreted literally. As it stands, that class is the equivalent to [ABCDEF]. If you mean just the three characters A, - or F then [A\-F] will do what you want, but it is usual to put the hyphen at the start or end of the class list to make it unambiguous. [-AF] and [AF-] are the same as [A\-F] and rather more readable

Upvotes: 3

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