Shell Programming and Scripting

diff -b --side-by-side --suppress-common-lines file1 file2

awk '
    { gsub( "^.", "& " ); }   # needed if leading "<" isnt always separated by whitespace from rest of line
    /^</ {
        if( old[$2] )
            printf( "%s  old=\"%s\"  new=\"%s\"\n", $2, old[$2], $3 );
        else
            new[$2] = $3;
    }
    /^>/ {
        if( new[$2] )
            printf( "%s  old=\"%s\"  new=\"%s\"\n", $2, $3, new[$2] );
        else
            old[$2] = $3;
    }
'  input >output

abc  old="10"  new="15"
xyz  old="02"  new="05"

awk '

# lines of awk programme
' diff.out

printf( "%s  old=\"%s\"  new=\"%s\"\n", $2, $3, new[$2] )

awk:cmd line:11 (filename=input.txt FNR=4) fatal:division by zero

printf( "%s  old=\"%s\"  new=\"%s\"\n", $2, $3, new[$2] ) > output.txt