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merged 2 commits into from
Feb 7, 2016
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[ExpressionLanguage] Add caution about backslash handling #6241

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07f8e40
[components][expression_language] Add doc for backslashes
zerustech Jul 29, 2015
31d74e5
Add a caution about backslash escaping
wouterj Feb 7, 2016
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Add a caution about backslash escaping
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@wouterj
wouterj committed Feb 7, 2016
commit 31d74e5d2577436e27f765bafb594678bb1348d0
34 changes: 12 additions & 22 deletions components/expression_language/syntax.rst
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Expand Up @@ -20,6 +20,18 @@ The component supports:
* **booleans** - ``true`` and ``false``
* **null** - ``null``

.. caution::

A backslash (``\``) must be escaped by 4 backslashes (``\\\\``) in a string
and 8 backslashes (``\\\\\\\\``) in a regex::

echo $language->evaluate('"\\\\"'); // prints \
$language->evaluate('"a\\\\b" matches "/^a\\\\\\\\b$/"'); // returns true

Control characters (e.g. ``\n``) in expressions are replaced with
whitespace. To avoid this, escape the sequence with a single backslash
(e.g. ``\\n``).

.. _component-expression-objects:

Working with Objects
Expand Down Expand Up @@ -181,28 +193,6 @@ Comparison Operators
You must use parenthesis because the unary operator ``not`` has precedence
over the binary operator ``matches``.

A backslash(``\``) must be escaped by 4 backslashes(``\\\\``) in a string and
8 backslashes(``\\\\\\\\``) in a regex::

$language->evaluate('"\\\\"');
// returns \

$language->evaluate('"a\\\\b" matches "/^a\\\\\\\\b$/"');
// returns true

Control characters must be defined as the escaped form of their escape sequences.
Otherwise, they will be replaced by spaces and ignored::

$language->evaluate('"a\nb"');
// returns a b

$language->evaluate('"a\\nb"');
// returns a\nb

This is because the backslashes in a string will be stripped by the
``stripcslashes()`` function and the stripped slashes in a regex will be
stripped again by the regex engine.

Examples::

$ret1 = $language->evaluate(
Expand Down