The following characters have special meaning in search patterns:
Many utilities support POSIX character lists, which are useful for matching non-ASCII characters in languages other than English. These lists are recognized only within [] ranges. A typical use would be [[:lower:]], which in English is the same as [a-z].
The following table lists POSIX character lists:
| Notation | Action |
|---|---|
| [:alnum:] | Alphanumeric characters |
| [:alpha:] | Alphabetic characters, uppercase and lowercase |
| [:blank:] | Printable whitespace: spaces and tabs but not control characters |
| [:cntrl:] | Control characters, such as ^A through ^Z |
| [:digit:] | Decimal digits |
| [:graph:] | Printable characters, excluding whitespace |
| [:lower:] | Lowercase alphabetic characters |
| [:print:] | Printable characters, including whitespace but not control characters |
| [:punct:] | Punctuation, a subclass of printable characters |
| [:space:] | Whitespace, including spaces, tabs, and some control characters |
| [:upper:] | Uppercase alphabetic characters |
| [:xdigit:] | Hexadecimal digits |
The following characters have special meaning in replacement patterns:
| Character | Meaning |
|---|---|
| \ | Turn off the special meaning of the character that follows. |
| \n | Restore the nth pattern previously saved by \( and \). n is a number from 1 to 9, matching the patterns searched sequentially from left to right. |
| & | Reuse the search pattern as part of the replacement pattern. |
| ~ | Reuse the previous replacement pattern in the current replacement pattern. |
| \e | End replacement pattern started by \L or \U. |
| \E | End replacement pattern started by \L or \U. |
| \l | Convert first character of replacement pattern to lowercase. |
| \L | Convert replacement pattern to lowercase. |
| \u | Convert first character of replacement pattern to uppercase. |
| \U | Convert replacement pattern to uppercase. |
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