Or store those patterns in a file, one per line and run grep -f that-file - *.txt Or put patterns on several lines: grep - 'foo You can do this by preceding each pattern with the -e option. You need to pass the -E option to grep to select it (formerly that was done with the egrep separate command²) grep -E - 'foo|bar' *.txtĪnother possibility when you're just looking for any of several patterns (as opposed to building a complex pattern using disjunction) is to pass multiple patterns to grep. The portable way is to use the newer syntax, extended regular expressions. The old, default syntax ( basic regular expressions) doesn't support the alternation ( |) operator, though some versions have it as an extension, but written with a backslash. Second, grep supports at least¹ two syntaxes for patterns. If you do need a single quote, you can write it as '\'' (end string literal, literal quote, open string literal). (also note the - end-of-option-marker to stop some grep implementations including GNU grep from treating a file called -foo-.txt for instance (that would be expanded by the shell from *.txt) to be taken as an option (even though it follows a non-option argument here)). Single quotes prevent expansion of anything between them (including backslashes) the only thing you can't do then is have single quotes in the pattern. The easiest way to do that is to put single quotes around it. If you are looking for a Linux Developer job, check Jooble! Resourcesįull Text of Harrison Bergeron by Kurt Vonnegut, Jr.First, you need to protect the pattern from expansion by the shell. If you know of an different method feel free to post them in the comments. They all achieved the same results, but done in a different way. Here we examined three different ways to grep multiple strings from a file, pattern matching, basic regular expression and extended regular expressions. Some people find certain ways easier to remember, or just more efficient. There are always several ways to accomplish the same task in Linux. You can set an alias for grep to egrep for convenience. In extended regexp we do not need to escape the pipe because it is supported as an OR operator. Or, we can use egrep: egrep 'Pattern1|Pattern2' filename We can use the extended regexp by using the -E option with grep. grep 'motion\|winced' HarBerg.txt Using Extended Regular Expressions to Grep Multiple StringsĮxtended Regular Expressions support the OR operator. Here we will use the same patterns and text file as above, but using the basic regular expressions syntax. grep 'Pattern1\|Pattern2' filenameīasic regexp do not support the pipe ( | ) as an OR operator, so we have to escape it with a backslash. Here is an example of using basic regular expressions to find two strings in a file using grep. The grep command supports both basic and extended regular expressions. grep -e "winced" -e "motion" HarBerg.txt Using Basic Regular Expressions to Grep Multiple Strings Here is an example of searching for the word winced, and the word motion, in the text of the Harrison Bergeron short story that is saved as HarBerg.txt. You can specify several patterns by using the -e switch. Using Pattern Matching to Grep Multiple Strings This is not meant to be a regex primer, but they are an important tool for matching several patterns. Here we will discuss pattern matching, basic regular expressions and extended regular expression. As with everything in Linux, there are several ways to accomplish the same task. There are several ways you can match multiple strings or patterns from a file using grep.
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