 | Chapter 6 Pattern Matching |  |
| Chapter 6 Pattern Matching | |
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). |
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 |
