expr | usage |
/hello/ | looks for the string between the forward slashes (case-sensitive) |
/hello/i | looks for the string between the forward slashes (case-insensitive) |
/hello/g | looks for multiple occurrences of string between the forward slashes |
/h.llo/ | the '.' matches any one character other than a new line character... matches 'hello', 'hallo' but not 'h\nllo' |
/h.*llo/ | the "*" matches any character(s) zero or more times... matches "hello", "heeeeeello", "hllo", "hwarwareallo" |
/\d/ | matches any digit |
/\D/ | matches any non-digit |
/\w/ | matches any word character (a-z, A-Z, 0-9, _) |
/\W/ | matches any non-word character |
/\s/ | matches any white space character (\r (carriage return),\n (new line), \t (tab), \f (form feed)) |
/\S/ | matches any non-white space character |
/[abcd]/ | matches any character in square brackets |
/[ch]at/ | matches cat or hat |
/[^abcd]/ | matches anything except the characters in square brackets |
/[a-z]/ | matches all lowercase letters (a to z) |
/[A-Z]/ | matches all uppercase letters (A to Z) |
/[0-9]/ | matches all digits |
/[a-zA-Z]/ | matches all lowercase and uppercase letters |
/[^a-zA-Z]/ | matches non-letters |
/[a-zA-Z0-9]/ | matches all lowercase, uppercase letters and numbers |
/(hello){4}/ | matches "hellohellohellohello" |
/hello{3}/ | matches "hellooo" and "helloooo" but not "helloo" |
/(hello){1,3}/ | matches "hello" that occur between 1 and 3 times (inclusive) |
/(hello){3,}/ | matches "hello" that occur atleast 3 times |
/ab*c/ | matches zero or more repetitions of "b" (matches "abc", "abbbbc", "ac") |
/ab+c/ | matches one or more repetitions of "b" (matches "abc", "abbbbc", but not "ac") |
/^/ | matches beginning of a line |
/$/ | matches end of a line |
/(hard)?work/ | matches "work" or "hardwork" |
/(?:hard)?work/ | matches "work" or "hardwork" but is a non-capturing group |
/i am a (cat|dog|whale) person/ | matches "i am a cat person", "i am a dog person" and "i am a whale person" |
/z(?=a)/ | positive lookahead... matches the "z" before the "a" in pizza but not the first "z" |
/z(?!a)/ | negative lookahead... matches the first "z" but not the "z" before the "a" |
/(?<=[aeiou])\w/ | positive lookbehind... matches any word character that is preceded by a vowel |
/(?<![aeiou])\w/ | negative lookbehind... matches any word character that is not preceded by a vowel |