Last updated on August 22nd, 2018 at 04:06 am
grep command Means – globally search regular expression. It is very useful while searching for strings in Unix and Linux operating system. Here we would be taking a look on grep command in Unix with examples,Linux grep examples,grep command options,egrep command in Unix
grep command in unix with examples
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 … ]
grep 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*
- grep CAT tmpfile – search ‘tmpfile’ for ‘CAT’ anywhere in a line
- grep -i -w failure adpatch.log – grep case insensitive command .It search adpatch.log for word failure in any case
- grep run[- ]time *.txt – find ‘run time’ or ‘run-time’ in all txt file.txt
-
who | grep appmmgr – pipe who to grep, look for appmmgr
-
grep -r “oracle” * – grep recursive option .It search for oracle string in current directory files and all the files in sub directory
- 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$. |
| \ (Back Slash) | turn off the special meaning of the next character, as in \^. To look for a Caret “^” at the start of a line, the expression is ^\^. |
| [ ] (Brackets) | match any one of the enclosed characters, as in [aeiou]. Use Hyphen “-” for a range, as in [0-9]. |
| [^ ] | match any one character except those enclosed in [ ], as in [^0-9]. |
| . (Period) | match a single character of any value, except end of line. So b.b will match “bob”, “bib”, “b-b”, etc. |
| * (Asterisk) | match zero or more of the preceding character or expression. An asterisk matches zero or more of what precedes it. Thus [A-Z]* matches any number of upper-case letters, including none, while [A-Z][A-Z]* matches one or more upper-case letters. |
grep regex examples
grep kite file.txt {search file.txt for lines with ‘kite’}
grep ‘^kite’ file.txt {‘kite’ at the start of a line}
grep ‘kite$’ 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 in Unix
If you want to search multiple words in the same grep command ,then use egrep command in unix
| 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’ :
|
grep with pipe command
pipe command in Linux let u input the output of the one command to the another command.
Example
ps -ef|grep python
Here output of “ps -ef” command is input for the grep command
Conclusion
grep is a very useful command for search word,expression in the Unix operation system. Hope you like this post on grep command in Unix with examples
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