#!/usr/bin/env bash

# @(#) s1       Demonstrate filter one file with contents from another, grep

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
LC_ALL=C ; LANG=C ; export LC_ALL LANG
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C awk tee grep

FILE=${1-data1}

pl " Input data file $FILE:"
cat $FILE

pl " Input file data2:"
cat data2

pl " Amended input data file data3:"
awk '{ print $2,$1}' data2 |
tee data3

rm -f data4
pl " Results, filter data1, selecting data3 contents:"
grep -f data3 data1 |
tee data4
# rm -f data4   # test when grep does not create a file
pe
if [ -s data4 ] # true if file exists and size > 0
then
  while read line       # do some command for each filtered line
  do
    pe " Do your command here with line \"$line\""
  done < data4
else
  pe " No lines selected."
fi

exit 0

$ ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 3.16.0-4-amd64, x86_64
Distribution        : Debian 8.4 (jessie) 
bash GNU bash 4.3.30
awk GNU Awk 4.1.1, API: 1.1 (GNU MPFR 3.1.2-p3, GNU MP 6.0.0)
tee (GNU coreutils) 8.23
grep (GNU grep) 2.20

-----
 Input data file data1:
AA 3
BB 1
CC 3
DD 6
EE 2
FF 6

-----
 Input file data2:
1 EE
3 CC
2 AA
12 AF

-----
 Amended input data file data3:
EE 1
CC 3
AA 2
AF 12

-----
 Results, filter data1, selecting data3 contents:
CC 3

 Do your command here with line "CC 3"