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13.5. grepping for a List of Patterns

egrep (Section 13.4) lets you look for multiple patterns using its grouping and alternation operators (big words for parentheses and a vertical bar). But sometimes, even that isn't enough.

Both egrep and fgrep support a -f option, which allows you to save a list of patterns (fixed strings in the case of fgrep) in a file, one pattern per line, and search for all the items in the list with a single invocation of the program. For example, in writing this book, we've used this feature to check for consistent usage in a list of terms across all articles:

% egrep -f terms *

(To be more accurate, we used rcsegrep (Section 13.7), since the articles are all kept under RCS (Section 39.5), but you get the idea.)

-- TOR

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