Shell Programming and Scripting

A,B
1,2

C,D
4,5

A,B,C,D
1,2, ,
 , ,4,5

A,B,C,D
1,2,3,4

{
  printf "%s,%s\n" "$(head -1 file1)" "$(head -1 file2)"
  sed '2,$ s/$/,,/' file1
  sed '2,$ s/^/,,/' file2
} > output_file

A,B,C,D
1,2,,
,,4,5

File-1
A,B,C
1,2,3
4,5,6

A,C,D
2,3,4
0,1,2

Desired output
A,B,C,D
1,2,3,
4,5,6,
2,,3,4
0,,1,2

#!/bin/ksh
IAm=${0##*/}
if [ $# -lt 2 ]
then	printf 'Usage: %s file1 ... fileN\n' "$IAm" >&2
	exit 1
fi
awk '
BEGIN {	FS = OFS = ","
	# Gather field names from the 1st line of each input file...
	for(i = 1; i < ARGC; i++) {
		if((getline < ARGV[i]) != 1) {
			printf("*** Cannott read header from file \"%s\".\n",
			    ARGV[i])
			continue;
		}
		close(ARGV[i])
		for(j = 1; j <= NF; j++)
			if($j in H)
				continue;
			else {	H[$j] = ++Hc
				OH[Hc] = $j
				# Add to output file header.
				printf("%s%s", HOFS, $j)
				HOFS = OFS
			}
	}
	print ""
}
FNR == 1 {
	# Clear output order list and headers from from previous file.
	for(i in O)
		delete O[i]
	for(i in FH)
		delete FH[i]
	# Determine order in which input fields should be output for this file...
	for(i = 1; i <= NF; i++)
		FH[$i] = i
	for(i = 1; i <= Hc; i++)
		O[i] = (OH[i] in FH) ? FH[OH[i]] : NF + 1
	next
}
{	# Print the data lines for the current input file.
	for(i = 1; i <= Hc; i++)
		printf("%s%s", $O[i], (i == Hc) ? ORS : OFS)
}' "$@"

awk -f script.awk input1.csv input2.csv

awk ' BEGIN { FS =OFS=","
    ^ invalid char ''' in expression

default bash

ksh