There are many ways to use the grep command. It would print all the lines matching a certain pattern. It was a command used in a simple Unix text editor called ed(pronounced ee dee). As a consequence, any text after the caret symbol will be matched with lines starting by this text.įor example, in order to find all drives starting with “sd” (also called SCSI disks), you can use the caret symbol with grep.Grep is a commonly used command in Linux (or Unix) to search through 1 or more files for a pattern or word.įun fact: grep is short for Global regular expression print(g/re/p). ^ symbol : also called the caret symbol, this little hat symbol is used in order to define the beginning of a line.Most common regular expression patterns are detailed below with examples : The main difference between basic and extended regular expressions is the fact that you can use regular expressions symbols with BRE (basic regular expressions) but they will have to be preceded by a backslash. Grep supports two kinds of regular expressions : basic and extended regular expressions. Regular expressions are definitely a great tool to master : they allow users to search for text based on patterns like text starting with a specific letters or text that can be defined as an email address. One of the greatest features of the grep command is the ability to search for text using regular expressions. In order to find out this information, you can use the “ dmesg” command and pipe it to the grep command. Let’s say for example that you introduced a new disk into your system and you are not sure about the name given to this new disk. This is heavily used when performing troubleshooting operations on Linux systems because the kernel will write to its buffer ring when starting or booting up. Note : if you are not sure about how to use pipes on Linux, here’s a complete guide on input and output redirection.Īnother great usage of the grep command is to inspect the Linux Kernel buffer ring. If you are interested in bash processes for example, you can type the following command $ ps aux | grep bash You can pipe the “ ps” command with the “ grep” command in order to filter the processes you are interested in. $ grep root /etc/passwdĪnother very popular way of using the grep command is to look for a specific process on your Linux system.Īs explained in one of our previous tutorials, you have to use the “ ps” command in order to list all the processes currently running on your system. In order to find the root account in a specific file, simply enter your text and the file you want to search into. On Linux, as you already probably know it, user accounts are listed in a specific file called the passwd file. There are complex options that can be used with grep, but let’s start with a set of very quick examples. This is a great way to remember the grep syntax and the find syntax at the same time but the find syntax is the exact opposite : path first and expression after. In order to remember the syntax of the grep command, just remember that grep can be written as grEP which means that the expression comes before the path. Before listing and detailing all the options provided by grep, let’s have a quick way to memorize the syntax of the grep command.
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