Below are the most common grep commands with examples. Note: Grep is case-sensitive. Make sure to use the correct case when running grep commands. To print any line from a file that contains a specific pattern of characters, in our case phoenix in the file sample2 , run the command:.
Grep will display every line where there is a match for the word phoenix. When executing this command, you do not get exact matches. Instead, the terminal prints the lines with words containing the string of characters you entered. Here is an example:. Tip: If your search pattern includes characters other than alphanumeric, use quotation marks. This includes blank spaces or any symbol. To search multiple files with the grep command, insert the filenames you want to search, separated with a space character.
In our case, the grep command to match the word phoenix in three files sample , sample2 , and sample3 looks like this example:. The terminal prints the name of every file that contains the matching lines, and the actual lines that include the required string of characters. You can append as many filenames as needed. The terminal prints a new line with the filename for every match it finds in the listed files. Tip: Refer to our article Xargs Commands to learn how to use xargs with grep to search for a string in the list of files.
To search all files in the current directory, use an asterisk instead of a filename at the end of a grep command. The output shows the name of the file with nix and returns the entire line.
Grep allows you to find and print the results for whole words only. Steve Steve To add to Steve's excellent answer. It's intuitive that longer patterns are faster. If the pattern was one byte then grep would have to check every byte. If the pattern is 4-bytes then it could makes 4-byte skips. If the pattern was as long as text then grep would only do one step. Yes, it is intuitive -- if you understand how Boyer-Moore works.
Even otherwise it's intuitive. It would be easier to find a long needle in a haystack than a shorter one — RajatJ. The counter example to "being faster when longer" is cases where you have to do a lot of tests before you fail, and you can't move ahead anyway. Say the file xs. The Boyer-Moore-Horspool improvement to Boyer-Moore improves on the skip-ahead in that case, but it's probably not going to be only three machine instructions in the general case.
Tino thanks. Show 5 more comments. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. When you are ready to proceed, try the following command. This is nice, but if you were working with a large c file of something similar, it would probably be much more useful to you if the lines identified which line in the file they were, what way you could track down a particular string more easily, if you needed to open the file in an editor to make some changes.
This can be accomplished by ading the -n parameter:. Another interesting switch is -v, which will print the negative result. In other words, grep will print all of the lines that do not match the search string, rather than printing the lines that match it.
In the following case, grep will print every line that does not contain the string "boo," and will display the line numbers, as in the last example. The -c option tells grep to supress the printing of matching lines, and only display the number of lines that match the query. The -l option prints only the filenames of files in the query that have lines that match the search string.
This is useful if you are searching through multiple files for the same string. An option more useful for searching through non-code files is -i, ignore case. This option will treat upper and lower case as equivalent while matching the search string. In the following example, the lines containg "boo" will be printed out, even though the search string is uppercase. Setting up Tomcat and Java on Ubuntu.
If you need more assistance we offer Online Training and Onsite training as well as consulting. The grep command. This tutorial explains the usage of the grep command for searching for regular expressions in files. Grep Grep is a command line tool to search for regular expressions.
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