1.grep 's Regular Expression Metacharacters(Which I always dismissed~)
| [^] | Matches one character not in the set | '[^A–K]ove' | Matches lines not containing a character in the range A through K, followed by ove. |
| /< | Beginning-of-word anchor | '/<love' | Matches lines containing a word that begins with love. |
| /> | End-of-word anchor | 'love/>' | Matches lines containing a word that ends with love. |
| /(../) | Tags matched characters | '/(love/)ing' | Tags marked portion in a register to be remembered later as number 1. To reference later, use /1 to repeat the pattern. May use up to nine tags, starting with the first tag at the left-most part of the pattern. For example, the pattern love is saved in register 1 to be referenced later as /1. |
| x/{m/} x/{m,/} x/{m,n/} | Repetition of character x: m times, at least m times, or between m and n times | 'o/{5/}' 'o/{5,/}' 'o/{5,10/}' | Matches if line has 5 occurences of o , at least 5 occurences of o , or between 5 and 10 occurrences of o . |
Prints the line if it contains the word north. The /< is the beginning-of-word anchor, and the /> is the end-of-word anchor.
4.grep 's Options
| –b | Precedes each line by the block number on which it was found. This is sometimes useful in locating disk block numbers by context. |
| –c | Displays a count of matching lines rather than displaying the lines that match. |
| –h | Does not display filenames. |
| –i | Ignores the case of letters in making comparisons (i.e., upper-- and lowercase are considered identical). |
| –l | Lists only the names of files with matching lines (once), separated by newline characters. |
| –n | Precedes each line by its relative line number in the file. |
| –s | Works silently, that is, displays nothing except error messages. This is useful for checking the exit status. |
| –v | Inverts the search to display only lines that do not match. |
| –w | Searches for the expression as a word, as if surrounded by /< and />. This applies to grep only. (Not all versions of grep support this feature; e.g., SCO UNIX does not.)
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egrep (Extended grep )
The main advantage of using egrep is that additional regular expression metacharacters (see Table 3.4 ) have been added to the set provided by grep. The /(/) and /{/}, however, are not allowed. (See GNU grep –E if using Linux.)
Table 3.4. egrep 's Regular Expression Metacharacters
| ^ | Beginning-of-line anchor | '^love' | Matches all lines beginning with love. |
| $ | End-of-line anchor | 'love$' | Matches all lines ending with love. |
| . | Matches one character | 'l..e' | Matches lines containing an l, followed by two characters, followed by an e. |
| * | Matches zero or more characters | '*love' | Matches lines with zero or more spaces of the preceding characters followed by the pattern love. |
| [ ] | Matches one character in the set | '[Ll]ove' | Matches lines containing love or Love. |
| [^ ] | Matches one character not in the set | '[^A–KM–Z]ove' | Matches lines not containing A through K or M through Z, followed by ove. |
| New with egrep: |
| + | Matches one or more of the preceding characters | '[a–z]+ove' | Matches one or more lowercase letters, followed by ove. Would find move, approve, love, behoove, etc. |
| ? | Matches zero or one of the preceding characters | 'lo?ve' | Matches for an l followed by either one or not any occurrences of the letter o. Would find love or lve. |
| a|b | Matches either a or b | 'love|hate' | Matches for either expression, love or hate. |
| () | Groups characters | 'love(able|ly) (ov)+' | Matches for lovable or lovely. Matches for one or more occurrences of ov. |