Question

I am using the grep -f function to extract lines from a file which match a particular pattern. Let’s say my pattern file is pattern.txt, as follows.

1
2
3
4
5

And the file against which I am matching this pattern is file.txt,

1::anv
2::tyr
3::yui
4::fng
5::gdg
6::ere
7::rer
8::3rr
9::gty

Now when I do a grep -f pattern.txt file.txt, I am getting this ->

1::anv
2::tyr
3::yui
4::fng
5::gdg
8::3rr

The last line in the output above, is causing my problem. How do I modify this grep command so as to get the output (showing correct correspondences) as follows?

1::anv
2::tyr
3::yui
4::fng
5::gdg

Answer 1

Add ^ before your patterns so that grep will match a line start with your pattern. If your pattern is actually set of numbers, You don’t need a list of patterns. Just use ^[1-5]:.