¹ some grep implementations support even more like perl-compatible ones with -P, or augmented ones with -X, -K for ksh wildcards. To work around that, with some grep implementations like GNU grep, you can use the -H option, or with any implementation, you can pass /dev/null as an extra argument. Note that if *.txt expands to a single file, grep won't prefix matching lines with its name like it does when there are more than one file. 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. First, you need to protect the pattern from expansion by the shell.
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