Why do regexes and string literals use different escape sequences?
The handling of escape sequences varies across languages and between string literals and regular expressions. For example, in Python the \s escape sequence can be used in regular expressions but not in string literals, whereas in PHP the \f form feed escape sequence can be used in regular expressions but not in string literals.
In PHP, there is a dedicated page for PCRE escape sequences (http://php.net/manual/en/regexp.reference.escape.php) but it does not have an official list of escape sequences that are exclusive to string literals.
As a beginner in programming, I am concerned that I may not have a full understanding of the background and context of this topic. Are these concerns valid? Is this an issue that others are aware of?
Why do different programming languages handle escape sequences differently between regular expressions and string literals?
The escape sequences found in string literals are there to stop the programing language from getting confused. For example, in many languages a string literal is denoted as characters between quotes, like so
my_string = 'x string'
But if your string contains a quote character then you need a way to tell the programming language that this should be interpreted as a literal character
my_string = 'x's string' # this will cause bugs
my_string = 'x\'s string' # lets the programing language know that the internal quote is literal and not the end of the string
I think that most programing languages have the same set of escape sequences for string literals.
Regexes are a different story, you can think of them as their own separate language that is written as a string literal. In a regex some characters like the period (.) have a special meaning and must be escaped to match their literal counterpart. Whereas other characters, when preceded by a backslash allow those characters to have special meaning.
For example
regex_string = 'A.C' # match an A, followed by any character, followed by C
regex_string = 'A\.C' # match an A, followed by a period, followed by C
regex_string = 'AsC' # match an A, followed by s, followed by C
regex_string = 'A\sC' # match an A, followed by a space character, followed by C
Because regexes are their own mini-language it doesn't make sense that all of the escape sequences in regexes are available to normal string literals.
- Regular expression that ignores HTML entities
- Allow access to page only from certain referrer
- Regex to match string containing two names in any order
- Matching boot times from log using sed -E
- Validate Bangladeshi phone number with optional +88 or 01 preceeding 11 digits
- Split address and numbers
- Use dynamic (variable) string as regex pattern in dart
- Regular expression matching Android package name
- Replace commas not inside single quotes with an @ symbol
- Visual Studio Code Search and Replace with Regular Expressions
- Split string on commas not inside double quotes
- Replace inner letters inside words that start with and end with a specific letter with the same amount of a specific character
- regex for expression with one separator hyphen
- Extracting specific data from a string with regex and Powershell
- Parse datetime string in Ydm.His format
- Extract all words double wrapped in curly braces
- Parse dot-delimited video filename to extract show title, series number and episode number
- Split a string into words, preserving contractions but removing leading apostrophes from words
- Split string on pipes which are not between square braces
- Simple regex pattern for email
- How to extract filename without extension in Makefile
- Regex pattern containing backlashes causes failure in preg_replace()
- preg_replace() pattern starting with < and ending with > doesn't find HTML comments as intended
- Split a string on spaces and/or commas after a word which may be preceded by a small word
- How to convert split() to preg_split()?
- Parse a string without delimiters into a 2d array
- Regex to extract WordPress wp-config database information and automating it with ansible to update a shared hosting environment
- Input regex for UK postcodes constantly invalid
- Parsing a string representation of nested arrays into an Array
- Split a CSV where some entries have double quotes