Shell Programming and Scripting

UID,HD1,HD2,HD3,HD4
1,2,33,44,55
2,10,14,15,16

UID
HD1
HD4

UID,HD1,HD4
1,2,55
2,10,16

$ cols=($(sed '1!d;s/, /\n/g' $A | grep -nf $B | sed 's/:.*$//'))

$ cut -d ',' -f 1$(printf ",%s" "${cols[@]}") $A

sed '1!d;s/, /\n/g' $A

sed '1!d;s/,/\n/g' $A

#!/bin/ksh
A=A.txt
B=B.txt
cols=($(sed '1!d;s/,/\n/g' "$A" | grep -nf "$B" | sed 's/:.*$//'))
cut -d ',' -f 1$(printf ",%s" "${cols[@]}") "$A"

#!/bin/ksh
A='A.txt'
B='B.txt'
awk '
BEGIN {	FS = OFS = ","
}
FNR == NR {
	h[++hc] = $0
	next
}
FNR == 1 {
	for(i = 1; i <= hc; i++) {
		for(j = 1; j <= NF; j++) {
			if($j == h[i]) {
				o[i] = j
				break
			}
		}
		if(j > NF) {
			printf("Header \"%s\" not found in file \"%s\".\n",
			    h[i], FILENAME)
			exit 1
		}
	}
}
{	for(i = 1; i <= hc; i++)
		printf("%s%s", $o[i], (i == hc) ? ORS : OFS)
}' "$B" "$A"

# cat A.txt
UID,HD1,HD2,HD3,HD4
1,2,33,44,55
2,10,14,15,16
# cat B.txt
UID
HD1
HD4

# awk 'FNR==NR{h[$0]=$0;next}FNR==1{for(;i++<NF;){if($i==h[$i]){o[l++]=i}}}{for(_ in o)printf "%s%s",$o[_],(_==(l-1))?RS:FS}' FS=\, B.txt A.txt
UID,HD1,HD4
1,2,55
2,10,16