Compare two text files and print the difference against key in bash shell script

Question

Shell script, bash, have 2 large files around 1.2 GB data, with key and values, I need to compare both files based on the key and store difference in the value in the third file

Answer 1

Could you please try following, written and tested with shown samples(also considering that your Input_file(s) are not starting from spaces).

awk '
BEGIN{
  OFS=";"
}
{
  match($0,/ .*/)
  line=substr($0,RSTART,RLENGTH)
  sub(/^ +/,"",line)
}
FNR==NR{
  num=split(line,array,";")
  for(i=1;i<=num;i++){
    arrayfromFile2[$1]=(arrayfromFile2[$1]?arrayfromFile2[$1] OFS:"")array[i]
  }
  delete array
  next
}
($1 in arrayfromFile2){
  num=split(arrayfromFile2[$1],temparrayChkFile2,";")
  for(i=1;i<=num;i++){
    arrayChkFile2[temparrayChkFile2[i]]
  }
  num=split(line,array,";")
  for(i=1;i<=num;i++){
    if(!(array[i] in arrayChkFile2)){
       val=(val?val OFS:"")array[i]
    }
  }
  print $1" "val
  val=""
  next
}
1
'  Input_file2  Input_file1