Grep can search for a string in groups of files. To find a pattern that is more than one word long, enclose the string with single or double quotation marks: $ grep "Louisa May" extensions Pipes that list through grep, looking for the pattern May: $ ls -l *.ps | grep May The first part of this command line, ls -l *.ps ps" that were created in the month of May: $ ls -l *.ps | grep May The following example displays files ending in ". To use grep as a filter, you must pipe the output of the command through grep. It allows you to filter out useless information from the output of commands. Grep is very often used as a "filter" with other commands. Note that grep failed in the first try because none of the entries began with a lowercase "a." 4.1.1 grep as a Filter Grep is case-sensitive that is, you must match the pattern with respect to uppercase and lowercase letters: $ grep allan extensions Note that more than one line may match the pattern you give: $ grep Allan extensions Strings may include "white space," punctuation, and invisible (control) characters.įor example, to find Edgar Allan Poe's telephone extension, type grep, all or part of his name, and the file containing the information: $ grep Poe extensions Edgar Allan Poe x72836 Where string is the word or phrase you want to find, and file is the file to be searched.Ī string is one or more characters a single letter is a string, as is a word or a sentence. The basic syntax of the grep command is: $ grep string file The kill command can be substituted for any other command for example if you are running containers on an OpenVZ server and spot a bunch of suspect processes you can run them through vzpid to get the container id's of processes under a particular name to find the owner of those processes.To search for a particular character string in a file, use the grep command. Top -b -n1 | grep apache2 | awk '' | xargs killĪs we can see in the image above, top has been run in batch mode once, the output piped to grep to search for the apache2 string that output is then piped into awk which has printed only the process id's which have then been piped to xargs which has then ran the kill command on them 1 by 1, then searching for apache2 processes again they are gone confirming they were killed. Now how about if we want to grab just the process id's from the output? for that we add awk into the mix: ![]() This would be useful over the more commonly used watch command if you wanted to log the output to a file, for example: If we want to monitor these, for example, to see how much cpu time they are using we can up the number of times the batch mode in top runs: We can pipe the output of top in batch mode to grep to search for a string, in this case I will look for the apache2 processes. ![]() This command with do as it suggests run top in batch mode with the -b switch, the -n1 tells it to run 1 time, -n5 would be 5 times. In this post we will be looking at running top in batch mode, looking for a string with grep, grabbing the process id's with awk and sending the process id's to be processed by another command with xargs.įor speed, I have just set up a quick VPS and installed apache. Written by Anthony Smith, 7 July 2020 Article was migrated from WordPress to Vanilla in March 2022
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