Compare two files for matching lines and store positive results

I have two files.

File 1:

A0001  C001
B0003  C896
A0024  C234
.
B1542  C231
.
upto 28412 such lines

File 2:

A0001
A0024
B1542
.
.
and 12000 such lines.

I want to compare File 2 against File 1 and store the matching lines from File 1. I tried Perl and Bash but none seems to be working.

The latest thing I tried was something like this:

for (@q) # after storing contents of second file in an array
{
        $line =`cat File1 | grep $_`; #directly calling File 1 from bash
        print $line;
}

but it fails.

Answers:

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Method 1

This should do the job:

grep -Ff File2 File1

The -f File2 reads the patterns from File2 and the -F treats the patterns as fixed strings (ie no regexes used).

Method 2

You can use awk:

$ awk 'FNR==NR{a[$1];next}($1 in a){print}' file2 file1
A0001   C001
A0024   C234
B1542   C231

Method 3

It looks to me like both files are already sorted on the first field. If so:

join file1 file2

is best, by about as far as your files are large.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0