For years and years I thought the fgrep command was a shorthand for running grep with the -f flag (“Obtain patterns from FILE, one per line”). I thought this was a weird flag to promote to its own command; I never used it. Why did other people have all of these files full of regexes to search for but I’d never needed such a thing?

Life made so much more sense when I realized that fgrep was a shortcut not for grep -f but for grep -F, which interprets the given pattern as a plain string instead of as a regex. Okay, now that’s an option I’ve used plenty of times.

Here’s a thought experiment: if you had an alias for grep -f, how it would even work? The synopsis for this form of grep looks like

grep [OPTION...] -f PATTERN_FILE [FILE...]

Presumably the heretical fgrep would work like

fgrep [OPTION...] PATTERN_FILE [FILE...]

What if you had multiple pattern files, though? How would you distinguish them from the files to be searched? Maybe you could separate them with the -- dummy argument, like

fgrep patterns1 patterns2 -- file.txt

But in that case, how would a command like

fgrep filename1 filename2

be interpreted? Is filename2 a file to read patterns from or a file to search? If all filenames up to -- are assumed to be pattern files then suddenly the user needs to type a -- every single time they want to search a file! The only sane way to specify multiple pattern files would be to require an -f to precede each one after the first:

fgrep patterns1 -f patterns2 file.txt

This asymmetric syntax is definitely not an improvement on just typing out grep -f.