I need a regular expression able to match everything but a string starting with a specific pattern (specifically index.php and what follows, like index.php?id=2342343).
Solution 1
Regex: match everything but:
- a string starting with a specific pattern (e.g. any - empty, too - string not starting with
foo):- Lookahead-based solution for NFAs:
- Negated character class based solution for regex engines not supporting lookarounds:
- a string ending with a specific pattern (say, no
world.at the end):- Lookbehind-based solution:
- Lookahead solution:
- POSIX workaround:
- a string containing specific text (say, not match a string having
foo):- Lookaround-based solution:
- POSIX workaround:
- Use the online regex generator at www.formauri.es/personal/pgimeno/misc/non-match-regex
- a string containing specific character (say, avoid matching a string having a
|symbol): - a string equal to some string (say, not equal to
foo):- Lookaround-based:
- POSIX:
- a sequence of characters:
- PCRE (match any text but
cat):/cat(*SKIP)(*FAIL)|[^c]*(?:c(?!at)[^c]*)*/ior/cat(*SKIP)(*FAIL)|(?:(?!cat).)+/is - Other engines allowing lookarounds:
(cat)|[^c]*(?:c(?!at)[^c]*)*(or(?s)(cat)|(?:(?!cat).)*, or(cat)|[^c]+(?:c(?!at)[^c]*)*|(?:c(?!at)[^c]*)+[^c]*) and then check with language means: if Group 1 matched, it is not what we need, else, grab the match value if not empty
- PCRE (match any text but
- a certain single character or a set of characters:
- Use a negated character class:
[^a-z]+(any char other than a lowercase ASCII letter) - Matching any char(s) but
|:[^|]+
- Use a negated character class:
Demo note: the newline \n is used inside negated character classes in demos to avoid match overflow to the neighboring line(s). They are not necessary when testing individual strings.
Anchor note: In many languages, use \A to define the unambiguous start of string, and \z (in Python, it is \Z, in JavaScript, $ is OK) to define the very end of the string.
Dot note: In many flavors (but not POSIX, TRE, TCL), . matches any char but a newline char. Make sure you use a corresponding DOTALL modifier (/s in PCRE/Boost/.NET/Python/Java and /m in Ruby) for the . to match any char including a newline.
Backslash note: In languages where you have to declare patterns with C strings allowing escape sequences (like \n for a newline), you need to double the backslashes escaping special characters so that the engine could treat them as literal characters (e.g. in Java, world\. will be declared as "world\\.", or use a character class: "world[.]"). Use raw string literals (Python r'\bworld\b'), C# verbatim string literals @"world\.", or slashy strings/regex literal notations like /world\./.
Solution 2
You could use a negative lookahead from the start, e.g., ^(?!foo).*$ shouldn't match anything starting with foo.
Solution 3
You can put a ^ in the beginning of a character set to match anything but those characters.
[^=]*
will match everything but =
Solution 4
Just match /^index\.php/, and then reject whatever matches it.
Solution 5
In Python:
>>> import re
>>> p='^(?!index\.php\?[0-9]+).*$'
>>> s1='index.php?12345'
>>> re.match(p,s1)
>>> s2='index.html?12345'
>>> re.match(p,s2)
<_sre.SRE_Match object at 0xb7d65fa8>
