Escape Sequences¶
Escape sequences are sequences of characters with a special meaning. Most of the time, the literal value of the character displayed is its meaning, while, sometimes, there are other hidden meaning.
An escape sequence is dedicated to a technology, and they are rare the same between two technologies, or even, between two engines dedicated to that technology.
Here are some examples of escape sequences.
- PHP, in strings:
n (new line)
t (horizontal tabulation)
“ (double quote, inside a double quoted-string)
“ This is not an escape sequence : single quoted string do not recognize this
u{01f418} : a unicode codepoint, representing an elephpant
200 : a character in octal notation
x69 : a character in hexadecimal notation
- HTML :
´ (a acute accent)
"e; (double quote)
Escape sequences should not be confused with escape characters, though they are related : some escape sequences are introduced by an escape character. Others rely on a format.
<?php
// \1 is an escape sequence that represents the first capturing parenthsis.
// It is a special meaning for REGEX.
preg_match('/(.)\1/', $string);
// Displays AA
echo "A\101";
?>
See also String literals (MySQL), Lexical Structure (PostgreSQL), INI file