Next, let’s try to find the process of the powerHR application ( start.sh): $ pidof start.sh For example, we know on the *nix systems, the init process has the PID 1, so we can use pidof to verify it: $ pidof init A program name can be a command, script, or executable. Here, we pass the program name to the pidof command. First, of course, pidof needs to know what to find. It is well worth the time to learn more about this excellent command, especially some of its advanced features.As its name implies, the pidof command can find the PID of a running program. You can even make use of pipes for more complicated searches and filtering using grep. You can look for one or several patterns in a single file or many files, or use them to filter out the lines from those files containing those patterns. ConclusionĪ tool like grep is indeed extremely useful, not to mention indispensable, for looking through a multitude of text files, scripts, and especially logs for specific patterns with considerable ease. Also, do check out pdfgrep for searching through PDF files. I also added another pattern to filter out, “pci=nocrs”.There are more features in grep than what is covered here so if you plan to use grep regularly, do take the time to research what it can do, and how to better use it. ![]() In that picture, I filtered out the lines that contained patterns I didn’t want first, then I searched the output for what I wanted. The patterns I was filtering out were “ohci-pci”, and “ehci-pci”. What I’ve done is used grep to list all of the lines containing the whole word “pci” (used the -w parameter to match whole words only), piped the output to another grep command to filter out whatever patterns I did not want to see in the output. Two examples using the kernel log (/var/log/kern.log). Piping output from grep to be viewed in ‘less’ was an example. There is a trick that I sometimes use with pipes to search for patterns and filter out unwanted output as well. $ grep -r -n -f filter.txt resources/js > ~/result.txt Something A Little More Advanced $ grep -r -n -f filter.txt resources/js | less Or redirect its output to a text file to view later. So a good thing to do is to pipe the output to the ‘less’ command so you can scroll through the output in its entirety. Remember that using grep on a large file, or even multiple files can produce a lot of output. This file contains these patterns to search for:Īll lines containing at least one of these patterns will be shown on the terminal output. To look for more than one pattern, simply create a text file containing a list of patterns, one each line, to look for in a file or directory and use the -f parameter to load the file containing the patterns.$ grep -f ~/groups.txt /etc/group So the fourth grep command lists all of the occurrences of “unix” in all of the files in /etc and its subdirectories, where any errors are simply ignored. The next parameter, ‘-s’, tells grep to avoid reporting any errors, such as “Permission Denied” errors, to the output, so as not to pollute the output with errors. The directory, in this case, is the current one (/etc), denoted by the ‘.’. The first parameter, ‘-r’, tells grep to search through a directory recursively. Because the group file did not have “unix” as a whole word, there was no output. The third command is slightly different with the ‘-w’ parameter, which tells grep to match a whole word rather than a simple piece of text. ![]() The second command did the same, but with the -n parameter, it shows which line the pattern was found in a file. It returns all occurrences of unix_allsort (username for this computer) as a result. In this screenshot, I use grep to search for the word “unix” in the /etc/group file. Look at the terminal output for these commands: /etc$ grep unix group How to eliminate lines containing certain patterns from your search, and how to run multiple grep commands using pipes for more advanced filtering. This article will show you how to use grep when searching through text files for one or more patterns. ![]() Here, the patterns used will be simple text rather than regular expressions. The most common usage is for quickly searching a file for occurrences of a pattern, which can be in plain text, or in the form of a regular expression. This simply looks for a specified text, or pattern, in a file or an entire directory. ![]() Linux and UNIX systems come with a shell command known as ‘grep’.
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