Pipe output to use as the search specification for grep on Linux

Question

How do I pipe the output of grep as the search pattern for another grep?

As an example:

grep   | xargs grep          


        

Answer 1

Okay breaking the rules as this isn't an answer, just a note that I can't get any of these solutions to work.

% fgrep -f test file

works fine.

% cat test | fgrep -f - file
fgrep: -: No such file or directory

fails.

% cat test | xargs -ifoo grep foo file 
xargs: illegal option -- i
usage: xargs [-0opt] [-E eofstr] [-I replstr [-R replacements]] [-J replstr]
             [-L number] [-n number [-x]] [-P maxprocs] [-s size]
             [utility [argument ...]]

fails. Note that a capital I is necessary. If i use that all is good.

% grep "`cat test`" file

kinda works in that it returns a line for the terms that match but it also returns a line grep: line 3 in test: No such file or directory for each file that doesn't find a match.

Am I missing something or is this just differences in my Darwin distribution or bash shell?