How can I compare two files based on the value of the first column?

Question

I want to compare two files based on the value of their first column:

file1

aaa 23 3
bbb 56 6
ccc 45 2

file2

bbb m a
aaa a m
ccc m m

The output file should be:

aaa  a m
bbb  m a
ccc  m m

i.e., we need to print the 2nd and 3rd columns of the 2nd file with the first column order of first file.

Can anybody suggest an awk script for this?

Answer 1

Try this:

$ awk 'FNR==NR{a[$1]=$0;next};{print a[$1]}' file2 file1

Answer 2

This will be very slow for large files, but you could do

$ while read a rest; do grep -w $a file2; done < file1
aaa a m
bbb m a
ccc m m

A faster way, in Perl:

$ cat file1 | perl -lane '$k{$F[0]}=$_;
                END{
                  open(A,"file1");
                  while(<A>){/^(.+?)\s/; print $k{$1}}
               }' file2
aaa a m
bbb m a
ccc m m