Shell Programming and Scripting

A
B
D

START
A
B
C
END

START
M
K
L
END

START
A
C
D
END

START
A
B
C
END

START
A
C
D
END

awk -vRS= 'NR==FNR{for (i=1;i<=NF;i++) a[$i]=1;next}{for (i=1;i<=NF;i++) if ($i in a){print;next}}' file1 file2

[root@rhel ~]# cat f1
A
B
D
[root@rhel ~]# cat f2
START
A
B
C
END

START
M
K
L
END

START
A
C
D
END
[root@rhel ~]# awk -vRS= 'NR==FNR{for (i=1;i<=NF;i++) a[$i]=1;next}{for (i=1;i<=NF;i++) if ($i in a){print;next}}' f1 f2
START
A
B
C
END
START
A
C
D
END

$ cat set.awk

NR==FNR { SET[$1]++; next }

/START/ { for(X in ISET) delete ISET[X]; next }

/END/ {
        UNIQ="";        F=0

        for(X in ISET)
        if(SET[X])
        {
                F=1
                UNIQ = UNIQ "|" X
        }

        # If any of the input set is contained, and
        # this set hasn't been found before, print and record
        if(F && !U[UNIQ])
        {
                U[UNIQ]++;
                print "START"
                for(X in ISET)  print X;
                print "END\n"
        }

        next
}

$1 { ISET[$1]++ }

$ awk -f set.awk input data

START
A
B
C
END

START
A
C
D
END

$

awk 'NR==FNR{$1=$1;s=$0;next}{p=$0;gsub($1 "|" $NF,x,p)}p~s' RS= ORS='\n\n' OFS="\n|\n"  file1 file2