[Chapter 6] 6.4 Examples of Searching

6.4 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; e.g., 'pattern'.) When used with ed, ex, sed, and awk, regular expressions are usually surrounded by / (although any delimiter works). Here are some example patterns:

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, `egrep` or awk only.
[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).

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[23]?86	8086, 80286, or 80386
compan(y\|ies)	company or companies

ex or vi pattern	What does it match?
\<the	Words like theater or the.
the\>	Words like breathe or the.
\<the\>	The word the.

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\}	Social security number (nnn-nn-nnnn).

6.4.1 Examples of Searching and Replacing

The following examples 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 tab.

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`]*$/d	Delete blank lines, plus lines containing spaces or tabs.
:g/^[`tab`]*$/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.
:.,$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).

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.


6.3 Metacharacters		7. The Emacs Editor