Shell reads multiple files at the same time

Read two files at the same time, and combine their peers into one line Write to a combined file

shell script:

#!/bin/bash

#set -x
cd `dirname "$0"`/../
INAS_SCRIPT_ROOT=`pwd`



function make_if_no_existis_dir()
{

   local dir=$1

   if [ ! -e "${dir}"  ]
   then

           mkdir  -p  "${dir}"
   be

   return 0

}


function union2()
{
  local file_name1=$1
  local file_name2=$2

  local union_dir=${INAS_SCRIPT_ROOT}/file/union

  make_if_no_existis_dir ${union_dir}

  >${union_dir}/union.txt


 exec 3< "${INAS_SCRIPT_ROOT}/file/${file_name1}"
 exec 4< "${INAS_SCRIPT_ROOT}/file/${file_name2}"

 while read line1<&3 && read line2<&4
 do
         echo $line1 $line2 >> ${union_dir}/union.txt
 done


}

union2 $1 $2

a.txt content:

aaa
bbb
ccc
ddd
eee
fff

b.txt content:

AAA
BBB
CCC
DDD
EEE
FFF
GGG

run script 

sh union_file.sh  a.txt b.txt

get the merged file union.txt

aaa aaa
BBB BBB
ccc CCC
ddd DDD
eee EEE
fff FFF
ggg GGG

Reference link: https://www.cnblogs.com/tangxin-blog/p/6531812.html