What I cannot find in the on-line docs

Its an operator thing, not a regex thing --- from perlop under "Binding Operators": 

...
       If the right argument is an expression rather than a
       search pattern, substitution, or transliteration, it is
       interpreted as a search pattern at run time.  This can be
       less efficient than an explicit search, because the pat-
       tern must be compiled every time the expression is evalu-
       ated.

[download]

This can sometimes cause problems for newcomers, especially when they use split with a double-quoted string as the split pattern (as seems to happen with undue frequency) and have an escaped metacharacter in the pattern: 

    $_ = 'this has a | pipe';
    @a = split /\|/;           # good
    print join(":", @a),"\n"; 
    @a = split "\|";           # oops
    print join(":", @a),"\n";

[download]

In the second case, the double-quoted string is first evaluated and the *resulting* string (sans backslash) is then used as the pattern in the regex.

In reply to Re: Regex without 'm' or '/' by danger
in thread Am I on the pipe, or what? by BorgCopyeditor

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