What is Regex?
A Regular Expression (RegEx) is a sequence of characters that defines a search pattern
Metachracters
Metacharacters are characters that are interpreted in RegEx engine.
[] ^ . $ * + ? {} () \ |
Square Brackets []
Square brackets specifies a set of characters you wish to match.
Caret ^
- Caret is used to check if a string starts with a certain character.
- At the starting of Square Bracket, inverts the sequence.
Period .
A period matches any single character in the given sequence.
Dollar $
The Dollar symbol is used to check if a string ends with a certain character.
Star *
The star symbol matches zero or more occurrences of the pattern left to it.
Plus +
The plus symbol matches one or more occurrences of the pattern left to it.
Question Mark ?
The question mark symbol matches zero or one occurrence of the pattern left to it.
Braces {}
{x,y}. This means at least x, and at most y repetitions of the pattern left to it
Alteration |
Basically the OR Operator
Group ()
Parentheses is used to group sub-patterns
Backslash \
Backlash is used to escape various characters including all meta-characters
Special Sequences
- \A - Matches if the specified characters are at the start of a string.
- \b - Matches if the specified characters are at the beginning or end of a word.
- \B - Opposite of \b. Matches if the specified characters are not at the beginning or end of a word.
- \d - Matches any decimal digit.
- \D - Matches any non-decimal digit.
- \s - Matches where a string contains any whitespace character.
- \S - Matches where a string contains any non-whitespace character.
- \w - Matches any alphanumeric character (digits and alphabets).
- \W - Matches any non-alphanumeric character.
- \Z - Matches if the specified characters are at the end of a string.