![]() ![]() +: The preceding character is matched one or more times. ?: The preceding character is optional and matched at most once. e.g x* will match the preceding x zero or more times. * : Matches zero or more instances of a character. : used to match ranges e.g matches all uppercase letters The ^ character is used to match the beginning of a pattern. To get all lines starting with 104 we could write, grep "^104" test.txt Given a file we can use grep and regular expressions to match a string. Regex matching.Ī regex pattern is a string of characters used to specify a pattern matching rule. The output of this command is all occurrences of the string Lubin in the file. With grep we can decide to get all words matching the string regardless of the string case by using the i option as follows. Notice that when we previously searched for a string, the search string had to be in the same case as the string in the file otherwise the search would not work. The command when executed on the test.txt file won't output anything because there is no full word mail in it. We use the w option with grep to match full words as shown grep -w "mail" test.txt We get all lines with mail string highlighted, however, we may need to match full words. When we run the following command, grep "mail" test.txt The output is all occurrences of gmail in all files in the current directory. We could also search all files in a directory by using the * option. The output of this command is all occurrences of search string and for each occurrences the file name is written at the beginning of the each line in the output. We can also use grep to search for a string in multiple files by writing, grep "search string" file1.txt file2.txt The output is all lines without the string worker. Inversely we could get lines in the file that don't match the string worker by using the v option as shown below, grep -v "worker" test.txt ![]() ![]() The output of thus command is all occurrences of the word worker highlighted. To search the test.txt file for the string worker we could write grep "worker" test.txt The basic use of grep is searching for strings in a file. Throughout this article we shall run the grep commands on the file below. Once a match is found it is printed as output. This text patterns is referred to as a regular expression. We use it to search for a specific pattern of characters in a file. Grep is an acronym for global regular expression print. The grep command is one of the most useful commands in a linux system for searching for text or patterns in a given file. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |