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The output will include matching lines prefixed by the full path to the file:
#Grep command linux how to
Here is an example showing how to search for the string in all files inside the /etc directory: grep -r /etc , instead of -r, use the -R option (or -dereference-recursive). When this option is used grep will search through all files in the specified directory, skipping the symlinks that are encountered recursively. To recursively search for a pattern, invoke grep with the -r option (or -recursive). If you don’t want that line to be shown pass the output to another grep instance as shown below. As you can see in the output above there is also a line containing the grep process. You can also chain multiple pipes in on command. Using Grep to Filter the Output of a Command #Ī command’s output can be filtered with grep through piping, and only the lines matching a given pattern will be printed on the terminal.įor example, to find out which processes are running on your system as user www-data you can use the following psĬommand: ps -ef | grep www-data www-data 18247 12675 4 16:00 ? 00:00:00 php-fpm: pool www To display the lines that do not match a pattern, use the -v ( or -invert-match) option.įor example, to print the lines that do not contain the string nologin you would use: grep -v nologin /etc/passwd root:x:0:0:root:/root:/bin/bashĬolord:x:124:124::/var/lib/colord:/bin/false If the string includes spaces, you need to enclose it in single or double quotation marks: grep "Gnome Display Manager" /etc/passwd Invert Match (Exclude) # The output should look something like this: root:x:0:0:root:/root:/bin/bash The most basic usage of the grep command is to search for a string (text) in a file.įor example, to display all the lines containing the string bash from the /etc/passwdįile, you would run the following command: grep bash /etc/passwd To be able to search the file, the user running the command must have read access to the file. Following picture show the example for the line numbers.The items in square brackets are optional. This will help user to go the line when user open the file in vi editer to know nearby logs. grep display with Line numbers: grep with option -n print the line number where the search text is present.Following picture show the example where we can see error (small letter) appeared two time in the log file an Error (with captil ‘E’) appeared 22 time in the event-log file. count option is case sensitive, be sure about the actual search string. This is useful when we want to know how many time one particular error happen in the log file. grep with count: grep with option -c search and provide the number of count for a text or string appeared in the file.
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For example if you want to search error in a file, you can put error or Error in search text will ingore and provide all related matching lines.
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-n : Display the matched lines and their line numbers.-i : Ignores upper/lower case for matching.-h : Display the matched lines, but do not display the filenames.-c : This prints a count of the lines that match the pattern.
#Grep command linux windows
grep does not work in the Windows environment.grep user requires read/write permissions to access the desired files and directories.grep requires access to a terminal/command line.egrep, and fgrep are other similar tools.The grep command is handy tool for searching known text or string through large log files.
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