Last updated on November 27th, 2016 at 01:11 pm
grep command Means – globally search regular expression. It is very useful while searching for strings in Unix /linix operating syste. Here we would be taking a look on linux grep command examples, how to use grep command in unix/linux
how to use grep command in unix
The grep utility searches text file.txt for a pattern and prints all lines that contain that pattern.
Syntax: grep [ -options ] limited-regular-expression [filename … ]
options:
| -c | Print only a count of the lines that contain the pattern. |
| -i | Ignore upper/lower case distinction during comparisons. |
| -l | Print only the names of file.txt with matching lines,separated by NEWLINE characters. Does not repeat the names of file.txt when the pattern is found more than once. |
| -n | Precede each line by its line number in the file (first line is 1). |
| -v | Print all lines except those that contain the pattern. |
| -r | It recursively search the pattern in all the file.txt in the current directory and all it’s subdirectory. |
| -w | It searches the exact word |
Unix grep command Examples
1: To find all uses of the word “top” (in any case) in the multiples file like x*, and write with line numbers:
grep -i -n top x*
2. grep CAT tmpfile – search ‘tmpfile’ for ‘CAT’ anywhere in a line
3. grep -i -w failure adpatch.log – search adpatch.log for word failure, any case
4. grep run[- ]time *.txt – find ‘run time’ or ‘run-time’ in all txt file.txt
5. who | grep appmmgr – pipe who to grep, look for appmmgr
6. grep -r “oracle” * – It search for oracle string in current directory files and all the files in sub directory
7. ps -ef|grep -v oracle – It will not show the lines which has oracle string in it
Understanding Regular Expressions:
| ^ (Caret) | match expression at the start of a line, as in ^A. |
| $ (Question) | match expression at the end of a line, as in A$. |
| \ (Back Slash) | turn off the special meaning of the next character, as in \^. To look for a Caret “^” at the start of a line, the expression is ^\^. |
| [ ] (Brackets) | match any one of the enclosed characters, as in [aeiou]. Use Hyphen “-” for a range, as in [0-9]. |
| [^ ] | match any one character except those enclosed in [ ], as in [^0-9]. |
| . (Period) | match a single character of any value, except end of line. So b.b will match “bob”, “bib”, “b-b”, etc. |
| * (Asterisk) | match zero or more of the preceding character or expression. An asterisk matches zero or more of what precedes it. Thus [A-Z]* matches any number of upper-case letters, including none, while [A-Z][A-Z]* matches one or more upper-case letters. |
unix/Linux grep command examples
grep kite file.txt {search file.txt for lines with ‘kite’}
grep ‘^kite’ file.txt {‘kite’ at the start of a line}
grep ‘kite$’ file.txt {‘kite’ at the end of a line}
grep ‘^kite$’ file.txt {lines containing only ‘kite’}
grep ‘\^s’ file.txt {lines starting with ‘^s’, “\” escapes the ^}
grep ‘[Kk]ite’ file.txt {search for ‘kite’ or ‘Kite’}
grep ‘T[oO][mM]’ file.txt {search for TOM, Tom, TOm or ToM }
grep ‘^$’ file.txt {search for blank lines}
grep ‘[0-9][0-9]’ file {search for pairs of numeric digits}
grep ‘^From: ‘ /usr/mail/$USER {list your mail}
grep ‘[a-zA-Z]’ {any line with at least one letter}
grep ‘[^a-zA-Z0-9] {anything not a letter or number}
grep ‘^.$’ {lines with exactly one character}
grep ‘”kite”‘ {‘kite’ within double quotes}
grep ‘”*kite”*’ {‘kite’, with or without quotes}
grep ‘^\.’ {any line that starts with a Period “.”}
grep ‘^\.[a-z][a-z]’ {line start with “.” and 2 lower case letters} letters.
egrep command
If you want to search multiple words in the same grep command ,then use egrep command
| It search all the three words in the file
egrep ‘cat|bad|sat’ file.txt
It discarded all the lines having any of these three word from the output of ps -ef ps -ef| egrep -v ‘cat|bad|sat’ :
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