Syntax Summary
Table 11-1 summarizes the syntax of regular expressions available in all versions of Tcl:
| . | Matches any character. |
| * | Matches zero or more instances of the previous pattern item. |
| + | Matches one or more instances of the previous pattern item. |
| ? | Matches zero or one instances of the previous pattern item. |
| ( ) | Groups a subpattern. The repetition and alternation operators apply to the preceding subpattern. |
| | | Alternation. |
| [ ] | Delimit a set of characters. Ranges are specified as [x-y]. If the first character in the set is ^, then there is a match if the remaining characters in the set are not present. |
| ^ | Anchor the pattern to the beginning of the string. Only when first. |
| $ | Anchor the pattern to the end of the string. Only when last. |
Advanced regular expressions, which were introduced in Tcl 8.1, add more syntax that is summarized in Table 11-2:
| {m} | Matches m instances of the previous pattern item. |
| {m}? | Matches m instances of the previous pattern item. Nongreedy. |
| {m,} | Matches m or more instances of the previous pattern item. |
| {m,}? | Matches m or more instances of the previous pattern item. Nongreedy. |
| {m,n} | Matches m through n instances of the previous pattern item. |
| {m,n}? | Matches m through n instances of the previous pattern item. Nongreedy. |
| *? | Matches zero or more instances of the previous pattern item. Nongreedy. |
| +? | Matches one or more instances of the previous pattern item. Nongreedy. |
| ?? | Matches zero or one instances of the previous pattern item. Nongreedy. |
| (?:re) | Groups a subpattern, re, but does not capture the result. |
| (?=re) | Positive look-ahead. Matches the point where re begins. |
| (?!re) | Negative look-ahead. Matches the point where re does not begin. |
| (?abc) | Embedded options, where abc is any number of option letters listed in Table 11-5. |
| c | One of many backslash escapes listed in Table 11-4. |
| [: :] | Delimits a character class within a bracketed expression. See Table 11-3. |
| [. .] | Delimits a collating element within a bracketed expression. |
| [= =] | Delimits an equivalence class within a bracketed expression. |
Table 11-3 lists the named character classes defined in advanced regular expressions and their associated backslash sequences, if any. Character class names are valid inside bracketed character sets with the [:class:] syntax.
| alnum | Upper and lower case letters and digits. |
| alpha | Upper and lower case letters. |
| blank | Space and tab. |
| cntrl | Control characters: u0001 through u001F. |
| digit | The digits zero through nine. Also d. |
| graph | Printing characters that are not in cntrl or space. |
| lower | Lowercase letters. |
| The same as alnum. | |
| punct | Punctuation characters. |
| space | Space, newline, carrage return, tab, vertical tab, form feed. Also s. |
| upper | Uppercase letters. |
| xdigit | Hexadecimal digits: zero through nine, a-f, A-F. |
Table 11-4 lists backslash sequences supported in Tcl 8.1.
| a | Alert, or “bell”, character. |
| A | Matches only at the beginning of the string. |
| Backspace character, u0008. | |
| B | Synonym for backslash. |
| cX | Control-X. |
| d | Digits. Same as [[:digit:]] |
| D | Not a digit. Same as [^[:digit:]] |
| e | Escape character, u001B. |
| f | Form feed, u000C. |
| m | Matches the beginning of a word. |
| M | Matches the end of a word. |
| Newline, u000A. | |
| Carriage return, u000D. | |
| s | Space. Same as [[:space:]] |
| S | Not a space. Same as [^[:space:]] |
| Horizontal tab, u0009. | |
| uXXXX | A 16-bit Unicode character code. |
| v | Vertical tab, u000B. |
| w | Letters, digit, and underscore. Same as [[:alnum:]_] |
| W | Not a letter, digit, or underscore. Same as [^[:alnum:]_] |
| xhh | An 8-bit hexidecimal character code. Consumes all hex digits after x. |
| y | Matches the beginning or end of a word. |
| Y | Matches a point that is not the beginning or end of a word. |
| Matches the end of the string. | |
| NULL, u0000 | |
| x | Where x is a digit, this is a back-reference. |
| xy | Where x and y are digits, either a decimal back-reference, or an 8-bit octal character code. |
| xyz | Where x, y and z are digits, either a decimal back-reference or an 8-bit octal character code. |
Table 11-5 lists the embeded option characters used with the (?abc) syntax.
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