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P5quotemeta - Implement Perl's quotemeta() built-in
use P5quotemeta; # exports quotemeta()
my $a = "abc";
say quotemeta $a;
$_ = "abc";
say quotemeta;
This module tries to mimic the behaviour of the quotemeta function ofi Perl as closely as possible.
quotemeta EXPR
quotemeta
Returns the value of EXPR with all the ASCII non-"word" characters
backslashed. (That is, all ASCII characters not matching
"/[A-Za-z_0-9]/" will be preceded by a backslash in the returned
string, regardless of any locale settings.) This is the internal
function implementing the "\Q" escape in double-quoted strings.
(See below for the behavior on non-ASCII code points.)
If EXPR is omitted, uses $_.
quotemeta (and "\Q" ... "\E") are useful when interpolating
strings into regular expressions, because by default an
interpolated variable will be considered a mini-regular
expression. For example:
my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
$sentence =~ s{$substring}{big bad wolf};
Will cause $sentence to become 'The big bad wolf jumped over...'.
On the other hand:
my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
$sentence =~ s{\Q$substring\E}{big bad wolf};
Or:
my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
my $quoted_substring = quotemeta($substring);
$sentence =~ s{$quoted_substring}{big bad wolf};
Will both leave the sentence as is. Normally, when accepting
literal string input from the user, quotemeta() or "\Q" must be
used.
In Perl v5.14, all non-ASCII characters are quoted in
non-UTF-8-encoded strings, but not quoted in UTF-8 strings.
Starting in Perl v5.16, Perl adopted a Unicode-defined strategy
for quoting non-ASCII characters; the quoting of ASCII characters
is unchanged.
Also unchanged is the quoting of non-UTF-8 strings when outside
the scope of a "use feature 'unicode_strings'", which is to quote
all characters in the upper Latin1 range. This provides complete
backwards compatibility for old programs which do not use Unicode.
(Note that "unicode_strings" is automatically enabled within the
scope of a "use v5.12" or greater.)
Within the scope of "use locale", all non-ASCII Latin1 code points
are quoted whether the string is encoded as UTF-8 or not. As
mentioned above, locale does not affect the quoting of ASCII-range
characters. This protects against those locales where characters
such as "|" are considered to be word characters.
Otherwise, Perl quotes non-ASCII characters using an adaptation
from Unicode (see <http://www.unicode.org/reports/tr31/>). The
only code points that are quoted are those that have any of the
Unicode properties: Pattern_Syntax, Pattern_White_Space,
White_Space, Default_Ignorable_Code_Point, or
General_Category=Control.
Of these properties, the two important ones are Pattern_Syntax and
Pattern_White_Space. They have been set up by Unicode for exactly
this purpose of deciding which characters in a regular expression
pattern should be quoted. No character that can be in an
identifier has these properties.
Perl promises, that if we ever add regular expression pattern
metacharacters to the dozen already defined ("\ | ( ) [ { ^ $ * +
? ."), that we will only use ones that have the Pattern_Syntax
property. Perl also promises, that if we ever add characters that
are considered to be white space in regular expressions (currently
mostly affected by "/x"), they will all have the
Pattern_White_Space property.
Unicode promises that the set of code points that have these two
properties will never change, so something that is not quoted in
v5.16 will never need to be quoted in any future Perl release.
(Not all the code points that match Pattern_Syntax have actually
had characters assigned to them; so there is room to grow, but
they are quoted whether assigned or not. Perl, of course, would
never use an unassigned code point as an actual metacharacter.)
Quoting characters that have the other 3 properties is done to
enhance the readability of the regular expression and not because
they actually need to be quoted for regular expression purposes
(characters with the White_Space property are likely to be
indistinguishable on the page or screen from those with the
Pattern_White_Space property; and the other two properties contain
non-printing characters).
Elizabeth Mattijsen [email protected]
Source can be located at: https://github.com/lizmat/P5quotemeta . Comments and Pull Requests are welcome.
Copyright 2018-2019 Elizabeth Mattijsen
Stolen from Zoffix Znet's unpublished String::Quotemeta, as found at:
https://github.com/zoffixznet/perl6-String-Quotemeta
This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.