Examples of Using Grep for Multiple Strings, Patterns and Words The pipe character | is also treated as a meta character in extended grep.
Grep wildcard operator how to#
To make sure you understand how to use grep to search multiple strings, we suggest creating a file with some text on which we are going to try out a couple of different use cases. We stored the file in the directory of the test user, that is, in /home/test/sample.txt How to Grep Multiple Patterns in a File In our case, we named the file sample.txt and added a few paragraphs of text. In the examples below, we will use grep instead of extended grep. Do not forget to use the backslash before the pipe character. Since grep does not support the pipe symbol as the alternation operator, you need to use the escape character (backslash \) to tell the grep command to treat the pipe differently.įor example, to search for the words extraand valuein the sample.txt file use this command: grep 'extra\|value' sample.txt Without passing any option, grep can be used to search for a pattern in a file or group of files. Note that single or double quotes are required around the text if it is more than one word. You can also use the wildcard () to select all files in a directory.
The output highlights the string you wanted to grep.Grep patterns are regular expressions (aka regex, regexp, RE), basic regular expressions (BRE) unless one of -E/ -F/ -P/ -K/ -X option (only the first two of which being standard) is used. * is a regexp operator that matches 0 or more of the preceding atom. In BREs, when at the start of the pattern or when following the ^ or \( regexp operators, it matches a literal * only (it's also taken literally inside bracket expressions). So grep '*README.md*' matches on lines that contain a literal * followed by README followed by any single character (the. (the ^s showing what within the line is matched by the regular expression, which you could see with -color) Since any number includes 0, that's functionally equivalent to grep '*README.m' (which would make no difference to which lines are being matched, only on what may be matched within the line (which would show with the -color option of GNU grep for instance)).įor instance, it would match on those 2 lines: *README mike regexp operator) followed by m followed by any number of ds. Here, it seems you're confusing regular expressions with shell wildcard patterns. The * wildcard operator which matches on 0 or more characters can be written. Therefore, the following command would match every line in the file : grep ' ' report7 UNIX Documentation Avoids the Term Wildcard In cards, a wildcard.
Would again be the same as: grep 'README\.md'Īs grep looks for a match within the line as opposed to finding lines that match the pattern exactly (for which you need -x). So with that grep implementation, you can do: grep -K 'README.md' With ast-open grep, which is also ksh93's grep builtin (not always built-in by default, and you need to enable it by putting /opt/ast/bin ahead of $PATH), you can use the -K option for grep to use shell wildcards (extended ksh93 ones). To match on lines that contain README.md. With that same implementation, wildcard matching can also be enabled within extended ( -E), augmented ( -X) or perl-like ( -P) regular expressions with the (?K) operator (and \(?K\) in basic regular expressions which actually breaks POSIX conformance, so I wouldn't rely on it as it could be removed in a future version).
With any modern grep implementation, you can also do: grep -F README.mdįor a fixed-string search (where.
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