You can invert the matching functionality of grep to return lines that don't contain matches of a pattern by adding the -v flag. If packages.json contained vUE that would be returned also. This will return lines contain matches of vue Vue and VUE This is useful when you don't know whether the text you are searching for will contain capital letters. The -i flag will make the grep command case insensitive. To change the way grep behaves and thus the results returned you can add optional flags before the pattern. Depending on your system the pattern may be highlighted in the output. Grep will return every line that contains the exact text vue in the file package.json. The most basic way to use grep is to match a literal text pattern in a single file.
The grep command syntax firstly takes a list of options, the pattern and then the files to search. While this guide is focused towards Linux you will be able to use the same commands on other popular Unix-like operating systems such as macOS.
In this article we will take a detailed look at how to use the grep command to search files in Linux and provide practical real-world examples. Its name stands for Global regular expression print and you can use it to search for patterns in files across your system.
It is best to get into the habit of enclosing pattern argument in single-quotes when invoking grep to ensure the pattern is received as intended. Note that certain punctuation characters such as * and $ have special meaning to the shell and may get transformed before passing these arguments along to the program. match all words that are exactly 7 letters long.match all words that start with k and end with k.Here are some suggested exercises to use as practice in forming regular expressions: try grep joy /usr/share/dict/words or grep 'b.b' /usr/share/dict/words and see which words matched. This file is a good one to grep for practice, e.g. We can instead search grep "binky(.*)" program.cĪ dictionary word list is available on myth in the file /usr/share/dict/words. Grep is smart enough to backtrack after this failed match, and tries to match b* to the next longest string, b so that the final b in the search string can match the final b in the text.īuilding on the binky example from earlier, consider the case where binky() actually takes a number of arguments, so matching on "binky()" will not suffice. For example, when using ab*b to match abb, if one matches the b* to bb, then there is no text left to match the final b to. However, naive greedy matching strategy will sometimes miss matches.
So therefore, ab* tries to match as many bs as possible instead of not matching any bs at all. This means that it tries to match as many characters as possible. Note that the * symbol does what we call greedy matching. * matches zero or more repeats of char to left of *Į.g., 'ab*'' matches 'abbbbb' and also 'a' Here are some of the core metacharacters that you will often use. grep especially shines is in matching complex patterns expressed as regular expressions (commonly shortened to regex). There is more to grep than just normal text matching. The general syntax for grep is grep įor example, if we were looking for all the lines where the binky function is called, we could use grep to search the source file as follows: grep "binky()" program.c Grep works like "find in file" (Ctrl-F or Command-F) search in Microsoft Word, or a search box on your computer's files and folders. Written by Chris Gregg, Prasanna Vasudevan and Rahul Agarwal, with modifications by Nick Troccoli