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Help: Fix documentation of escape sequences in a regex

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Documentation added by commit 4b35dab891 (Help: Document how escape
sequences work in a regex, 2018-07-18) is only correct for backslashes
inside `[]` groups.  The regex engine does interpret `\` escapes
elsewhere.  Fix the docs.

Inspired-by: R2RT <artur.ryt@gmail.com>
Fixes: #18428
This commit is contained in:
Brad King
2018-10-08 11:46:22 -04:00
parent fd02538974
commit fab2c2339b
1 changed files with 13 additions and 6 deletions
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19
Help/command/string.rst
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@@ -121,6 +121,11 @@ The following characters have special meaning in regular expressions:
Matches at end of input
``.``
Matches any single character
``\<char>``
Matches the single character specified by ``<char>``. Use this to
match special regex characters, e.g. ``\.`` for a literal ``.``
or ``\\`` for a literal backslash ``\``. Escaping a non-special
character is unnecessary but allowed, e.g. ``\a`` matches ``a``.
``[ ]``
Matches any character(s) inside the brackets
``[^ ]``
@@ -151,12 +156,9 @@ has lower precedence than concatenation. This means that the regular
expression ``^ab+d$`` matches ``abbd`` but not ``ababd``, and the regular
expression ``^(ab|cd)$`` matches ``ab`` but not ``abd``.
Backslash (``\``) characters in regular expressions are interpreted
literally and do not escape anything or represent placeholders.
However, CMake language :ref:`Escape Sequences` such as ``\t``,
``\r``, ``\n``, and ``\\`` may be used to construct literal tabs,
carriage returns, newlines, and backslashes (respectively) to pass
in a regex. For example:
CMake language :ref:`Escape Sequences` such as ``\t``, ``\r``, ``\n``,
and ``\\`` may be used to construct literal tabs, carriage returns,
newlines, and backslashes (respectively) to pass in a regex. For example:
* The quoted argument ``"[ \t\r\n]"`` specifies a regex that matches
any single whitespace character.
@@ -164,6 +166,11 @@ in a regex. For example:
a single forward slash ``/`` or backslash ``\``.
* The quoted argument ``"[A-Za-z0-9_]"`` specifies a regex that matches
any single "word" character in the C locale.
* The quoted argument ``"\\(\\a\\+b\\)"`` specifies a regex that matches
the exact string ``(a+b)``. Each ``\\`` is parsed in a quoted argument
as just ``\``, so the regex itself is actually ``\(\a\+\b\)``. This
can alternatively be specified in a :ref:`bracket argument` without
having to escape the backslashes, e.g. ``[[\(\a\+\b\)]]``.
Manipulation
^^^^^^^^^^^^