Section 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. Tables 6-6 through Table 6-9 show some example patterns.

Table 6-6. General search patterns

Pattern	What does it match?
bag	The string bag anywhere in the line
^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 anywhere in the line.
b[aeiou]g	b , a vowel, and g .
b[^aeiou]g	b , a consonant (or uppercase or symbol), and g .
b.g	b , any character, and g .
^...$	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, anywhere on the line
"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.

Table 6-7. egrep and awk search patterns

egrep or awk pattern	What does it match?
[567]	One of the digits 5 , 6 , or 7 .
fivesixseven	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(yies)	company or companies .

Table 6-8. ex and vi search 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 .

Table 6-9. ed, sed and grep search 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.

6.4.1. Examples of Searching and Replacing

The examples in Table 6-10 show the metacharacters available to sed and vi . We have shown vi commands with an initial colon because that is how they are invoked with vi . A space is marked by a ; a tab is marked by tab .

Table 6-10. Searching and replacing

Command	Result
s/.*/( & )/	Redo the entire line, but add parentheses.
s/.*/mv & &.old/	Change a word list (one word per line) into mv commands.
/^$/d	Delete blank lines.
:g/^$/d	Same as previous, in vi editor.
/^[ tab ]*$/d	Delete blank lines, plus lines containing only spaces or tabs.
:g/^[ tab ]*$/d	Same as previous, in vi 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, here are 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 \([Dd]o\)/ or /  Transpose, using hold buffers