![]() You can use grep to display all the lines that DO NOT match the given pattern. grep -C 5 search_pattern filename Show the lines that do not match ![]() The command below will show 5 lines before the matching one, the matching line and 5 lines after the matching line. My favorite is the option -C because it shows lines that are before and after the matching ones. ![]() The command below will show 5 lines before the matching ones along with the matching line(s). Similarly, you can use the -B option to show lines before the matching ones. The command below will show the matching lines along with the 5 lines after the match. You can use the -A to show lines after the matching ones. But when you are troubleshooting something, it helps to see a couple of lines before and/or after the matching lines. Show lines before and after the matching linesīy default, you only see the matching lines. This way, grep will return lines that match both Holmes and holmes. You can ignore case matching with the -i option: grep -i search_pattern filename Case insensitive searchīy default, the search with grep is case-sensitive. Let's see a few common use cases of the grep command. You probably already know that to search for a particular text or pattern in a file, you have to use grep like this: grep search_pattern filename I have included a PDF cheatsheet which you can download, print and keep on your desk. It's good if you are already familiar with the grep command but you keep forgetting which option does what. I'll just the common options and their explanation here. Linux Handbook already has a detailed article on grep, so I won't go in depth here. This article lists the most common grep commands with quick examples. However, you'll end up using a handful of grep commands most of the time. You probably will never need or use all of them. The grep command has a huge number of options and use cases. It's especially helpful when you are troubleshooting or debugging. Each line returned will be prefaced with the name of the file where the match was found.īy using pipes and/or redirection, you can use the output from any of these commands with other Unix tools, such as more, sort, and cut.Grep is a powerful UNIX command that lets you search inside the file contents on a variety of parameters. This command would search files with names such as myfile, my.hw1, and mystuff in the current directory. For example, if you wanted to find lines containing "dog" in any of the files in your directory with names beginning with "my", you could enter: fgrep dog my* You can also use wildcards to instruct fgrep to search any files that match a particular pattern. If you want to search for lines that contain any of several different words, you can create a second file (named secondfile in the following example) that contains those words, and then use the -f option: fgrep -f secondfile myfile To list the lines of myfile that do not contain "dog", use the -v option: fgrep -v dog myfile You can use the -i option with the grep command to match both upper- and lowercase letters: grep -i dog myfile The fgrep command is case sensitive specifying "dog" will not match "Dog" or "DOG". To search for several words separated by spaces, enclose the whole search string in quotes, for example: fgrep "dog named Checkers" myfile You can use the -w option with the grep command to return only lines where "dog" is included as a separate word: grep -w dog myfile This will also return lines where "dog" is embedded in larger words, such as "dogma" or "dogged". For example, to list all the lines of a file named myfile in the current directory that contain the word "dog", enter at the Unix prompt: fgrep dog myfile You can use fgrep to find all the lines of a file that contain a particular word. The general syntax of the grep commands is: For most purposes, you'll want to use fgrep, since it's generally the fastest. The tools in the grep family are very similar, and all are used for searching the contents of files for information that matches particular criteria. The grep utilities are a family of Unix tools, including grep, egrep, and fgrep, that perform repetitive searching tasks. ![]()
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