I am using regular expressions in Perl scripts and need to look at reference document frequently.

If you are writing Perl scripts and using regular expressions, you need to bookmark this Perl official reference document: "perlre - Perl regular expressions".

Even if you are using regular expressions in other programming languages, this Perl regular expressions reference document is still very useful, since other programming languages support regular expression in almost the same was as Perl.

Topics covered in "perlre - Perl regular expressions" include:

    NAME
    DESCRIPTION
        Modifiers
        Regular Expressions
        Quoting metacharacters
        Extended Patterns
        Special Backtracking Control Verbs
        Backtracking
        Version 8 Regular Expressions
        Warning on \1 Instead of $1
        Repeated Patterns Matching a Zero-length Substring
        Combining RE Pieces
        Creating Custom RE Engines
        PCRE/Python Support
    BUGS
    SEE ALSO