In this post, we will talk about the various symbols and what do they mean in the making of a regular expression. So, let’s see them one by one –
| Subexpression | Matches |
|---|---|
| \^ | Start of a string/line |
| $ | End of a string/line |
| \b | Word boundary |
| \B | Not a word boundary |
| \A | Beginning of entire string |
| \z | End of entire string |
| \Z | End of entire string (except allowable final line terminator) |
| . | Any one character (except line terminator) |
| […] | Any one character from listed one |
| [\^…] | Any one character from not the listed one |
Please see this post to understand the working of above Symbols.
Let’s now move to Normal( greedy ), Reluctant (non-greedy), and Possessive (very greedy) quantifiers
Normal(greedy) Quantifiers –
| Subexpression | Matches |
|---|---|
| {m,n} | Matches from m to n repetitions |
| {m,} | Matches m or more repetitions |
| {m} | Matches exactly m repetitions |
| {,n} | Matches from 0 to n repetitions (Short for {0,n}) |
| \* | Matches 0 or more repetitions (Short for {0,}) |
| + | Matches 1 or more repetitions (Short for {1,}) |
| ? | Matches exatcly 0 or 1 repetition (Short for {0,1}) |
Reluctant (non-greedy) Quantifiers –
| Subexpression | Matches |
|---|---|
| {m,n}? | Reluctant quantifier for “from m to n repetitions” |
| {m,}? | Reluctant quantifier for “m or more repetitions” |
| {m}? | Reluctant quantifier for 0 up to n repetitions |
| \*? | Reluctant quantifier: 0 or more |
| +? | Reluctant quantifier: 1 or more |
| ?? | Reluctant quantifier: 0 or 1 times |
Possessive (very greedy) quantifiers –
| Subexpression | Matches |
|---|---|
| {m,n}+ | Possessive quantifier for “from m to n repetitions” |
| {m,}+ | Possessive quantifier for “m or more repetitions” |
| {m}+ | Possessive quantifier for 0 up to n repetitions |
| \*+ | Possessive quantifier: 0 or more |
| ++ | Possessive quantifier: 1 or more |
| ?+ | Possessive quantifier: 0 or 1 times |
Now lets see various escapes and shorthands in regular expression
Escapes and Shorthands –
| Subexpression | Matches |
|---|---|
| \ | Escape (quote) character: turns most metacharacters off; turns subsequent alphabetic into metacharacters |
| \Q | Escape (quote) all characters up to \E |
| \E | Ends quoting begun with \Q |
| \t | A Tab character |
| \r | Return (carriage return) character |
| \n | ANewline character |
| \f | A Form feed |
| \w(small w) | Character in a word (use w+ for a word) |
| \W(Capital w) | A nonword character |
| \d(small d) | A Numeric digit (use \d+ for an integer) |
| \D(capital d) | A nondigit character |
| \s(small s) | A Whitespace character |
| \S(capital s) | A nonwhitespace character |