![]() This is a very powerful feature, if you can use use regular expression effectively. Match regular expression in files Syntax: So it matches all the words such as “the”, “THE” and “The” case insensitively as shown below.Īnd this is the last line. This searches for the given string/pattern case insensitively. Case insensitive search using grep -i Syntax: $ cp demo_file demo_file1ĭemo_file:this line is the 1st lower case line in this file.ĭemo_file:Two lines above this line is empty.ĭemo_file1:this line is the 1st lower case line in this file.ĭemo_file1:Two lines above this line is empty.ĭemo_file1:And this is the last line. When the Linux shell sees the meta character, it does the expansion and gives all the files as input to grep. The grep output will also include the file name in front of the line that matched the specific pattern as shown below. For this example, let us copy the demo_file to demo_file1. This is also a basic usage of grep command. Checking for the given string in multiple files. The basic usage of grep command is to search for a specific string in the specified file as shown below. Search for the given string in a single file This Line Has All Its First Character Of The Word With Upper Case.Īnd this is the last line. This line is the 1st lower case line in this file. THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE. In this article let us review 15 practical examples of Linux grep command that will be very useful to both newbies and experts.įirst create the following demo_file that will be used in the examples below to demonstrate grep command. Earlier we discussed 15 practical examples for Linux find command, Linux command line history and mysqladmin command. This is part of the on-going 15 Examples series, where 15 detailed examples will be provided for a specific command or functionality. If you know exactly what you need to change, and you are dealing with a string that is safe to be replaced by another, you can speed up the process by using the commands shown here.īe extra careful with strings that may be common in your files: If you apply a global change that affects more than what you intended, you may have to revert to your backup copies (which you certainly have, right?).You should get a grip on the Linux grep command. The xargs command will receive each file name returned by the find command and apply the sed command. In this case, I use the find command with the parameter -type f to return only files and not directory names. type f | xargs sed -i 's/user_/admin_/g' For that, I use the find command again: find. In my example scenario, there are files in subdirectories that also need to be changed. Change strings in files in the current and subdirectories The /g at the end of the parameter means replace all occurrences in each file. Here, I used the sed command with the -i argument to make the changes in place. If I only wanted to change the strings in the files in the present directory, I could use: sed -i 's/user_/admin_/g' *.yml Change strings in files in the same directory ![]() Yes, regular expressions can get complex.įollowing are two ways you can change strings in multiple files simultaneously. In other scenarios, you may have to use regular expressions more elaborate than the example above to catch strings preceded by a comment ( #) followed by zero or more spaces or a mix of upper and lower case. Note: As the combination of find and xargs grep does not highlight the string user_ like in the first example, I added an extra grep command to highlight the string. In my example scenario, I have three files that contain references to variables user_name and user_home, which for some good reason I must change to admin_name and admin_home.īefore making any changes, I inspect the occurrences in the current directory: Think of the following examples as methods to perform these types of changes using only the command line instead of an IDE.īut you may also want to inspect the changes before applying them because-different from the IDE option-the command-line method is more immediate (no confirmation is asked, by default). In this case, you would have the option to confirm, case by case, which occurrence to replace (unless you are pretty sure that you really want to replace all). If you are using an integrated development environment (IDE), you probably already have a function for global search and replace in multiple files. How well do you know Linux? Take a quiz and get a badge.Linux system administration skills assessment.A guide to installing applications on Linux.Download RHEL 9 at no charge through the Red Hat Developer program.
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