Issue
I know that you can use regex in grep and use patterns from a file to search another file. But, can you combine these two options?
For example, from the file where the patterns come from (with the -f option for use patterns from a file), I only want to use the first column to search the second file.
I tried this:
grep -E '^(*)\b' -f file_1 file_2 > file_3
To grep the first column from file_1 with the * wildcard, but it is not working. Any ideas?
Solution
Grep doesn't use wildcards for patterns, it uses regular expressions, so (*) makes little sense.
If you want to extract the first column from a file, use cut -f1 or awk '{print $1}' (or sed or perl or whatever to extract it), the redirect to grep using the special - (i.e. standard input) as the source file:
cut -f1 file1 | grep -f- file_2 > file_3
Answered By - choroba
