[Chapter 6] 6.4 Examples of Searching

6.4 Examples of Searching

When used with grep or egrep , regular expressions should be surrounded by quotes. (If the pattern contains a $ , you must use single quotes; e.g., ' pattern ' .) When used with ed , ex , sed , and awk , regular expressions are usually surrounded by / , although (except for awk ) any delimiter works. The following tables show some example patterns.

6.4.1 General patterns

Pattern	What Does It Match?
`bag`	The string bag .
`^bag`	bag at the beginning of the line.
`bag$`	bag at the end of the line.
`^bag$`	bag as the only word on the 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; `ed` , `grep` , and `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; `egrep` or `awk` only.
`[[:upper:]]+`	Same; POSIX `egrep` or `awk` .
`[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 or space (not a letter or a number).
`[^[:alnum:]]`	Same, using POSIX character class.

6.4.2 Egrep and awk patterns

egrep or awk Pattern	What Does It Match?
`[567]`	One of the numbers 5 , 6 , or 7 .
`five\|six\|seven`	One of the words five , six , or seven .
`80[2-4]?86`	8086 , 80286 , 80386 , or 80486 .
`80[2-4]?86\|(Pentium(-II)?)`	8086 , 80286 , 80386 , 80486 , Pentium , or Pentium-II .
`compan(y\|ies)`	company or companies .

6.4.3 Ex and vi patterns

ex or vi Pattern	What Does It Match?
`\<the`	Words like theater or the .
`the\>`	Words like breathe or the .
`\<the\>`	The word the .

6.4.4 Ed, sed and grep patterns

ed, sed or grep Pattern	What Does It Match?
`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 ).
`$why$.*\1`	A line with two occurrences of why .
`$[[:alpha:]_][[:alnum:]_.]*$ = \1;`	C/C++ simple assignment statements.

6.4.5 Examples of Searching and Replacing

The examples in Table 6.3 show the metacharacters available to sed or ex . Note that ex commands begin with a colon. A space is marked by a ; a tab is marked by a tab .

Table 6.3: Searching and Replacing
Command	Result
`s/.*/( & )/`	Redo the entire line, but add parentheses.
`s/.*/mv & &.old/`	Change a wordlist (one word per line) into `mv` commands.
`/^$/d`	Delete blank lines.
`:g/^$/d`	Same as previous, in `ex` editor.
`/^[` tab `]*$/d`	Delete blank lines, plus lines containing only spaces or tabs.
`:g/^[` tab `]*$/d`	Same as previous, in `ex` editor.
`s/*//g`	Turn one or more spaces into one space.
`:%s/*//g`	Same as previous, in `ex` editor.
`:s/[0-9]/Item &:/`	Turn a number into an item label (on the current line).
`:s`	Repeat the substitution on the first occurrence.
`:&`	Same as previous.
`:sg`	Same, but for all occurrences on the line.
`:&g`	Same as previous.
`:%&g`	Repeat the substitution globally (i.e., on all lines).
`:.,$s/Fortran/\U&/g`	On current line to last line, change word to uppercase.
`:%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).

Finally, some sed examples for transposing words. A simple transposition of two words might look like this:

s/die or do/do or die/		 Transpose words

The real trick is to use hold buffers to transpose variable patterns. For example:

s/\([Dd]ie\) or \([Dd]o\)/\2 or \1/	 Transpose, using hold buffers