Help direct stdout to grep!

cat patterns | egrep -f foo

egrep -f foo < patterns

OS X uses BSD grep and Linux continues to use GNU grep.

You can use grep instead of egrep and this will still work. Tested it.

@VikingOSX

I think you have it backwards. In your command, you are using foo as a source for patterns and looking for them in patterns via stdin. says_anova wants to read patterns from stdin and look for them in foo.

@says_anova,

Why not just use the basic form "grep -f patterns foo"? If you were doing something more fancy than cat, that would be a problem.

I thought the OP wanted to look for patterns in foo, and if found, they are printed to stdout. Here is my result. Etresoft, did I overthink this?

says_anova does want to look for patterns in foo. Your command is looking in file patterns for the patterns found in file foo.

It is hard to see when the two files are so similar. I think if you add "doghouse" to foo and then add "dog" to patterns, then you should see the difference.

GNU grep (Lion and earlier) clearly has manpage content that recommends grep -f patterns foo as the correct approach to finding patterns in foo. If I follow your suggestion above, on Lion:

My previous post was on Mountain Lion with the BSD grep.