The -A flag denotes the lines that come after the search string and -B prints the output that appears before the search string. You can use the -A or -B to dislay number of lines that either precede or come after the search string. Output Displaying number of lines before or after a search pattern Using pipes For example, If you want to know if a certain package is installed in Ubuntu system execute $ dpkg -L | grep "package-name"įor example, to find out if OpenSSH has been installed in your system pipe the dpkg -l command to grep as shown $ dpkg -L | grep -i "openssh" The grep command can be used together with pipes for getting distinct output. NO results will be returned because we are not searching for a pattern but an exact word! Using pipes with grep Output However, if you try $ grep -w "open" welcome.txt Passing then -w flag will search for the line containing the exact matching word as shown $ grep -w "opensource" welcome.txt Output Search for exact matching word using the -w option To number the lines where the string pattern is matched, use the -n option as shown $ grep -n "Linux" welcome.txt Number the lines that contain the search pattern with -n option Output As you can see, grep has displayed the lines that do not contain the search pattern. Next, press Enter Output Now, to display the lines that don’t contain the string “Linux” run $ grep -v "Linux" welcome.txt
#GREP USAGE IN LINUX FULL#
Hit ESC on Vim editor, type a full colon followed by set nu Going back to our file, let us display the line numbers as shown. The –v option tells grep to invert its output, meaning that instead of printing matching lines, do the opposite and print all of the lines that don’t match the expression. The -v option instructs grep to print all lines that do not contain or match the expression. To invert the Grep output, use the -v flag. To count the total number of lines where the string pattern appears or resides, execute the command below $ grep -c "Linux" welcome.txt Count the lines where strings are matched with -c option Output Awesome isn’t’ it? The - i is normally used to display strings regardless of their case sensitivity. To ignore case sensitivity, use the -i flag and execute the command below $ grep -i "linux" welcome.txt Nothing from the output, right? This is because grepping could not find and match the string “linux” since the first letter is Lowercase. Now let’s try and search for the string in lowercase. In the above example, our search results gave us what we wanted because the string “Linux” was specified in Uppercase and also exists in the file in Uppercase.
If you wish to search for a string in your current directory and all other subdirectories, search using the - r flag as shown $ grep -r "string-name" * Output Searching for a string recursively in all directories
Example $ grep -color "free and opensource" welcome.txt
If you are working on a system that doesn’t display the search string or pattern in a different color from the rest of the text, use the -color to make your results stand out. If the file is located in a different file path, be sure to specify the file path as shown below $ grep "string" /path/to/fileĬolorizing Grep results using the -color option Output As you can see, grep has not only searched and matched the string “Linux” but has also printed the lines in which the string appears. To search for a string in a file, run the command below Syntax $ grep "string" file name Great! Now we are ready to perform a few grep commands and manipulate the output to get the desired results.
Linux has also made a name for itself in PCs.īeginners looking to experiment with Linux can get started with friendlier linuxĭistributions such as Ubuntu, Mint, Fedora and Elementary OS.
#GREP USAGE IN LINUX FREE#
Linux is a free and opensource Operating system that is mostly used byĭevelopers and in production servers for hosting crucial components such as webĪnd database servers. To demonstrate this, let’s create a text file welcome.txt and add some content as shown. Grep command can be used to find or search a regular expression or a string in a text file. In this guide, we will look at Common grep command usage with a few examples. Furthermore, the command comes pre-installed in every Linux distribution. In Linux and Unix Systems Grep, short for “global regular expression print”, is a command used in searching and matching text files contained in the regular expressions.
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