![]() Note that for the -o flag, there is no exclamation mark at the end of the output. Last but not least, we use the -o flag to print the matched pattern itself, i.e., Educative. grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a. Searching for Zub would not yield any results because the -n flag runs a case-sensitive search. ![]() Additionally, we use the -n flag to print the line number of the line, which contains EDUcative and zub. Subsequently, we use the -i flag to run a case-insensitive search for the sub-string EDUCative in our text file and print the string which contains it. The grep utility has a standard option, -n, which will cause it to prepend its ordinary output with the line number on which grep matched the pattern. In the example below, we use the echo command to create a text file, and write Educative!, Edpresso, and Sadzub on lines 1, 2, and 3, respectively. The -help flag is used to open the manual page of grep, which contains additional information about it. The ^ operator is used to output all those lines in file.txt which have pattern as their first word. The -v flags invert the search results, as it displays those strings in file.txt which do not contain pattern. The -n flag outputs the line number of the lines containing pattern alongside the line itself. The o flag displays only the matched pattern instead of displaying the entire string or line which contains it. The -w flag is used to output all those lines in file.txt containing pattern as a whole word and not as a sub-string. The -l flag outputs the name of all those files containing text with the word pattern in it as a string or sub-string. It displays all the lines in file.txt that contain the word paTTern, regardless of the alphabetical case as a string or sub-string. The -i flag makes sure that grep performs a case-insensitive search. The -c flag is used to output the number of lines in file.txt that contain the word pattern as a string or sub-string. In this shot, we go through the most frequently used arguments for grep. Users can select a functionality of their choice by setting the right flags or arguments. While we’re still on grep, let’s examine the /etc/sudoers file. Example: Remove comments and empty lines. ![]() In the next article, we’ll use sed to achieve the same thing we did here with grep. To do this, we’d need a file editor like ed. For example, grep -lZ outputs a zero byte after each file name instead of the usual newline. The grep command supports many functionalities. While grep can format the output on the screen, this command is unable to modify a file in place. n, -line-number Prefix each line of output with the 1-based line number within its input file. The GNU Core-utilities package is available on all Unix-like operating systems. You can check out all of these options by simply typing grep –help.The grep command is part of the GNU Core-utilities package and filters text files for a given character arrangement or pattern. The grep command is extremely powerful with many options. We found a match that was ‘free and open source’.So that was a quick and concise tutorial on how to use the grep command. grep -n ‘free.*source’ LinuxAndUbuntu.txtĪs you can see in the image above that we searched for a phrase that begins with free and ended with a source. For instance, if we wanted to search for all instances where a phrase begins with free and ends with source we could use the following command. If you wish to search for a phrase that starts and end with some specific expression you can do that using. You can see in the image below that along with the line numbers, the name of the file matching the pattern is also printed. I will use the following command for this. It would mean that grep must search in all files in that directory. ![]() Now if I wanted to search for a pattern or expression in all those files I would just put a * instead of the filename. It is in the same directory as my first file. Now I have created another file called LNU.txt which has the following lines of text as follows.
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