This is similar in function to just piping the output of the ‘ps’ command to grep. For example, you could use it to find the process ID of the SSH daemon: $ pgrep sshd Pgrep is a command to search for the name of a running process on your system and return its respective process IDs. This means you don’t have to escape special characters like you would with regular grep. ![]() It’s useful when you need to search for regular expression characters. This switch will interpret a pattern as a list of fixed strings, and try to match any of them. Let’s search a text document for strings that contain two consecutive ‘p’ letters: $ egrep p\ fruits.txt There’s a ton of different things you can do with this, but here’s an example of what it looks like to use a regular expression with grep. This switch will interpret a pattern as an extended regular expression. 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. The literal match works with alphabetic and numerical characters (as well as some special characters).Grep is a command-line tool that Linux users use to search for strings of text. The regex patterns that define the search for the exact match of a given string are called “literals.” The name comes from the fact that they match the pattern literally, character by character. Grep was actually searching using the very basic regular expression. In the previous grep examples, grep performed the search for a specific string in the given text file. In this section, we will showcase a handful of regex methods using grep. While it’s popular, different applications and programming languages implement regex slightly differently. There are numerous string-searching algorithms and tools that use regular expression (regex for short) for performing searches and replacing actions. Regular expression has its own structure and rules. ![]() The term “regular expression” is defined as a special string that describes the searching pattern. At the start of this guide, we mentioned that grep stands for global regular expression print.
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