How to search multiple search patterns from a file with grep

Question

If I search for multiple search strings in grep : usually just do:

grep "search1\|search2" somefolder/*.txt

but, what if I have 100 or more search strings? Can I say like this:

grep "stringPattern.txt" somefolder/*.txt

where stringPattern.txt is a file containing a list of words I need to search in *.txt.

Answer 1

grep has the -f flag exactly for this, use:

grep -f patternfile somefolder/*.txt

Where in the patternfile the search patterns are separated line by line.

Answer 2

you can also work with other way around. if you have 100 patterns to search, then make a list what you don't want to search if it is less than 100 patterns and make it in a file1.txt

grep -vf file1.txt somefolder/*.txt

Answer 3

I've used perl to do this, as you can use perl to build a regex from an array:

#!/usr/bin/perl

use strict;
use warnings;
open ( my $searchfile, '<', "searchfile.txt" ) or die $!; 

my @search_for = <$searchfile>; 
close ( $searchfile );

my $search_regex = join ( "|", map {quotemeta} @search_for ); 
   $search_regex = qr/$search_regex/; 

print "Regex: $search_regex\n"; 

foreach my $file ( glob ( "somefolder/*.txt" ) ) { 
    open ( my $check, '<', $file ) or die $!; 
    while ( <$check> ) {
        print if m/$search_regex/;
    }
    close ( $check );
}

Note - quotemeta will escape metacharacters, which is good if you want to search for things including backslashes, spaces etc. But bad if you want to specify regex patterns.