linux - replace string in a file with value from another file

Question

I have two files. One of them defines a set of number-value pairs as follows (fileA):

 1  asm
 2  assert
 3  bio
 4  bootasm
 5  bootmain
 6  buf
 7  cat
 8  console
 9  defs
10  echo

The other file contains a bunch of value pairings, as follows (fileB):

bio types
bio defs
bio param
bio spinlock
bio buf
bootasm asm
bootasm memlayout
bootasm mmu
bootmain types
bootmain elf
bootmain x86
bootmain memlayout
cat types
cat stat
cat user

I want to write a script that replaces the values on file B with their corresponding numbers from file A. It does not matter if it generates a new file or changes the existing file B.

Any ideas? Thanks

Answer 1

awk 'NR==FNR{a[$2]=$1;next}{$1=a[$1];}1' fileA fileB

NR==FNR{a[$2]=$1;next} => This is true when the fileA is processed. An associative array is formed where the index is the 2nd column with the 1st column as its value.

{$1=a[$1];} => When the second file is processed, Replace the 1st column with the appropriate value stored in the array.

1 => Print every line.