This command will replace “string1” with “string2” in all files relative to the present working directory: $ grep -rl 'string1'. Grep and replaceĪ grep command piped to sed can be used to replace all instances of a string in a file. $ grep -v string-to-exclude filenameĪs you can see in the screenshot, the string we excluded is no longer shown when we run the same command with the -v switch. To see the contents of a file but exclude patterns from the output, you can use the -v switch. Obviously, this will only work in situations where you’re not expecting the rest of the line to have any text at all. You can also use the -w switch, which will tell grep that the string must match the whole line. To avoid this, and search for strictly “apple”, you can use this command: $ grep "\" fruits.txt In our examples above, whenever we search our document for the string “apple”, grep also returns “pineapple” as part of the output. This command tells grep to be case sensitive except for the first letter. What if we want to search for a string where the first can be uppercase or lowercase, but the rest of the string should be lowercase? Ignoring case with the -i switch won’t work in this case, so a simple way to do it would be with brackets. You can avoid this by telling grep to ignore the case with the -i switch. Or, technically using egrep is even fewer keystrokes: $ egrep 'string1|string2' filenameīy default, grep is case sensitive, which means you have to be precise in the capitalization of your search string. There are a few different ways you can use an or condition with grep, but we will show you the one that requires the least amount of keystrokes and is easiest to remember: $ grep -E 'string1|string2' filename On modern Linux systems, you will find these switches available in the base grep command, but it’s common to see distributions support the other commands as well. Various grep switches were historically included in different binaries. Difference between grep, egrep fgrep, pgrep, zgrep Notice that we only needed to use quotes around the strings that contained spaces. Let’s try searching a text document for two different strings: $ grep -e 'Class 1' -e Todd Students.txt You can specify multiple patterns by using the -e switch. You can also use grep to find multiple words or strings. Here’s an example where we search a text document for a string. While you can use grep to search the output piped from other command-line tools, you can also use it to search documents directly. Grep will accept both single quotes and double quotes, so wrap your string of text with either. For example, what if we needed to search for the “My Documents” directory instead of the single-worded “Documents” directory? $ ls | grep 'My Documents' If you need to search for a string of text, rather than just a single word, you will need to wrap the string in quotes. So if grep returns nothing, that means that it couldn’t find the word you are searching for. If the Documents folder didn’t exist, grep wouldn’t return any output. $ ls | grep DocumentsĪs you can see in the screenshot above, using the grep command saved us time by quickly isolating the word we searched for from the rest of the unnecessary output that the ls command produced. Let’s look in our home directory for a folder called Documents.Īnd now, let’s try checking the directory again, but this time using grep to check specifically for the Documents folder. That’s something you would use the “ls” command for.īut, to make this whole process of checking the directory’s contents even faster, you can pipe the output of the ls command to the grep command. Say that you need to check the contents of a directory to see if a certain file exists there. Let’s look at some really common examples. You can use it to search a file for a certain word or combination of words, or you can pipe the output of other Linux commands to grep, so grep can show you only the output that you need to see. Grep is a command-line tool that Linux users use to search for strings of text.
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