UNIX for Dummies Questions & Answers

awk 'BEGIN {
        # Slurp in the entire file, indexed by the key for comparison later.
        while(getline <"file2") ARR[$1]=$0
}

{
        # Match from file2
        if(ARR[$1])
        {
                # Print all the arguments from file2.  Since the keys are the same,
                # this is effectively the same as substituting after.
                printf("%s ",ARR[$1]);
                # Print everything that comes after.
                for(N=2; N<=NF; N++)
                        printf(" %s", $N);
                printf("\n");
        }
        # Otherwise, print the line unchanged
        else print;
}' < file1

<inputfile >outputfile awk '{
...