Pattern Matching Quick Reference with Examples (Unix Power Tools, 3rd Edition)

32.21. Pattern Matching Quick Reference with Examples

Table 32-7. Special characters in search patterns

Pattern	What does it match?
.	Match any single character except newline.
`*`	Match any number (including none) of the single characters that immediately precede it. The preceding character can also be a regular expression. For example, since . (dot) means any character, `.*` means "match any number of any character."
`^`	Match the following regular expression at the beginning of the line.
`$`	Match the preceding regular expression at the end of the line.
`[ ]`	Match any one of the enclosed characters.
	A hyphen (`-`) indicates a range of consecutive characters. A caret (`^`) as the first character in the brackets reverses the sense: it matches any one character not in the list. A hyphen or a right square bracket (`]`) as the first character is treated as a member of the list. All other metacharacters are treated as members of the list.
`\`{`n,m``\}`	Match a range of occurrences of the single character that immediately precedes it. The preceding character can also be a regular expression. \{`n`\} will match exactly `n` occurrences, \{`n`,\} will match at least `n` occurrences, and \{`n``,m`\} will match any number of occurrences between `n` and `m`.
`\`	Turn off the special meaning of the character that follows (except for \{ and \(, etc., where it turns on the special meaning of the character that follows).
``	Save the pattern enclosed between $ and $ into a special holding space. Up to nine patterns can be saved on a single line. They can be "replayed" in substitutions by the escape sequences \1 to \9.
`\< \>`	Match characters at beginning (`\<`) or end (`\>`) of a word.
`+`	Match one or more instances of preceding regular expression.
`?`	Match zero or one instances of preceding regular expression.
`\|`	Match the regular expression specified before or after.
`(' )`	Apply a match to the enclosed group of regular expressions.

The characters in Table 32-8 have special meaning only in replacement patterns.

Table 32-8. Special characters in replacement patterns

Pattern	What does it do?
`\`	Turn off the special meaning of the character that follows.
`\``n`	Restore the `n`th pattern previously saved by `$` and `$`. `n` is a number from 1 to 9, with 1 starting on the left.
`&`	Reuse the string that matched the search pattern as part of the replacement pattern.
`\u`	Convert first character of replacement pattern to uppercase.
`\U`	Convert replacement pattern to uppercase.
`\l`	Convert first character of replacement pattern to lowercase.
`\L`	Convert replacement pattern to lowercase.

32.21.1. Examples of Searching

When used with grep or egrep, regular expressions are surrounded by quotes. (If the pattern contains a $, you must use single quotes from the shell; e.g., 'pattern'.) When used with ed, ex, sed, and awk, regular expressions are usually surrounded by / (although any delimiter works). Table 32-9 has some example patterns.

Table 32-9. Search pattern examples

Pattern	What does it match?
`bag`	The string `bag`.
`^bag`	`bag` at beginning of line.
`bag$`	`bag` at end of line.
`^bag$`	`bag` as the only word on line.
`[Bb]ag`	`Bag` or `bag`.
`b[aeiou]g`	Second letter is a vowel.
`b[^aeiou]g`	Second letter is a consonant (or uppercase or symbol).
`b.g`	Second letter is any character.
`^...$`	Any line containing exactly three characters.
`^\`.	Any line that begins with a . (dot).
`^\.[a-z][a-z]`	Same, followed by two lowercase letters (e.g., troff requests).
`^\.[a-z]\{2\}`	Same as previous, grep or sed only.
`^[^.]`	Any line that doesn't begin with a . (dot).
`bugs*`	`bug`, `bugs`, `bugss`, etc.
`"word"`	A word in quotes.
`"word"`	A word, with or without quotes.
`[A-Z][A-Z]*`	One or more uppercase letters.
`[A-Z]+`	Same, extended regular expression format.
`[A-Z].*`	An uppercase letter, followed by zero or more characters.
`[A-Z]*`	Zero or more uppercase letters.
`[a-zA-Z]`	Any letter.
`[^0-9A-Za-z]`	Any symbol (not a letter or a number).
`[567]`	One of the numbers `5`, `6`, or `7`.
Extended regular expression patterns:
`five\|six\|seven`	One of the words `five`, `six`, or `seven`.
`80[23]?86`	One of the numbers `8086`, `80286`, or `80386`.
`compan(y\|ies)`	One of the words `company` or `companies`.
`\<the`	Words like `theater` or `the`.
`the\>`	Words like `breathe` or `the`.
`\<the\>`	The word `the`.
`0\{5,\}`	Five or more zeros in a row.
`[0-9]\{3\}-[0-9]\{2\}-[0-9]\{4\}`	U.S. Social Security number (`nnn``-nn-nnnn`).

32.21.2. Examples of Searching and Replacing

Table 32-10 shows the metacharacters available to sed or ex. (ex commands begin with a colon.) A space is marked by ; a TAB is marked by tab.

Table 32-10. Search and replace commands

Command	Result
`s/.*/( & )/`	Redo the entire line, but add parentheses.
`s/.*/mv & &.old/`	Change a word list into mv commands.
`/^$/d`	Delete blank lines.
`:g/^$/d`	ex version of previous.
`/^[``tab``]*$/d`	Delete blank lines, plus lines containing only spaces or TABs.
`:g/^[``tab``]*$/d`	ex version of previous.
`s/`*//g	Turn one or more spaces into one space.
`:%s/`*//g	ex version of previous.
`:s/[0-9]/Item &:/`	Turn a number into an item label (on the current line).
`:s`	Repeat the substitution on the first occurrence.
`:&`	Same.
`:sg`	Same, but for all occurrences on the line.
`:&g`	Same.
`:%&g`	Repeat the substitution globally.
`:.,$s/Fortran/\U&/g`	Change word to uppercase, on current line to last line.
`:%s/.*/\L&/`	Lowercase entire file.
`:s/\<./\u&/g`	Uppercase first letter of each word on current line (useful for titles).
`:%s/yes/No/g`	Globally change a word to `No`.
`:%s/Yes/~/g`	Globally change a different word to `No` (previous replacement).
`s/die or do/do or die/`	Transpose words.
`s/$[Dd]ie$ or $[Dd]o$/\2 or` `\1/`	Transpose, using hold buffers to preserve case.

-- DG