awk - How to compare two files that are partially matching and replace the parts that are matching in bash? -

i have 2 dat files, file1 , file2. first 1 has (for example) 1000 lines , second 100 lines. lines in both files have same format, i.e. 5 numbers, separated space. lines values of file2 partially matching lines file1. example, there line in file2 is:

1 2 3 4 5 

and there line in file1 is:

1 2 3 9 5 

it 4th value not matching. 1st, 2nd, 3rd , 5th values match. want in bash script. have started script far.

#! /bin/bash  #usage: sh ./script.sh test.dat check.dat   test_file=$1  check_file=$2 ## each line in test_file  while read line ;   arr=$(echo $line | tr " " "\n")  part_match=$(echo ${arr:0:8})  x=$(grep "$part_match" ${check_file})  ## here, if partial match exists in file2, save line in x. ## try substitute them awk or sed none of them works.   awk '{gsub(/${x}/, "${line}")}' check.dat > check_new.dat ## or  sed -i "s/$x/$line/pw" check.dat  done < ${test_file} 

none of them works. doing wrong? thank much!

"if partial match exists in file 2" - based on 0:8, if have partial match, have full match, because include 4th digit.

if want match on first 3 digits, should using 0:6.

the sed command not correct - either remove w flag or specify file name. edit original check.dat in place:

sed -i "s/$x/$line/p" check.dat 

or, write change check_new.dat, keeping check.dat

sed "s/$x/$line/pwcheck_new.dat" check.dat