Shell Programming and Scripting

$ cat text.txt
+12345678
text_A
+12345644
text_B
+12334241
text_C
+1234586
text_D
+12231241
text_E
+1234
text_F

$ cat head.txt
12345678	Head_A
12345644	Head_B
12334241	Head_C
1234	Head_F

$ cat outfile.txt
+12345678 Head_A
text_A
+12345644 Head_B
text_B
+12334241 Head_C
text_C
+1234	Head_F
text_F

awk 'FNR==NR{a[$1];next}{ for(i=1;i<=NF;i++){ if($i ~ "+" && $i in a) {print $i} else print $i} }' head.txt text.txt

awk '
        NR == FNR {
                i = substr($0,2);
                getline;
                A[i] = $0
                next
        }
        $1 in A {
                print "+" $0 RS A[$1]
        }
' text.txt head.txt

awk 'FNR==NR {h["+" $1]=$2;next} {print $0, h[$1]}' head.txt text.txt

awk 'FNR==NR {h["+" $1]=$2;next} $1 in h {print $0, h[$1]; getline; print}' head text
+12345678 Head_A
text_A
+12345644 Head_B
text_B
+12334241 Head_C
text_C
+1234 Head_F
text_F

awk 'FNR==NR {h[$1]=$2;next} $1 in h {print "+" $1, h[$1];print $2}' head.file RS="+" text.file

time awk 'FNR==NR {h["+" $1]=$2;next} $1 in h {print $0, h[$1]; getline; print}' text.txt header.txt > outA.tmp

real	0m20.552s
user	0m17.823s
sys	0m2.697s

time awk '
        NR == FNR {
                i = substr($0,2);
                getline;
                A[i] = $0
                next
        }
        $1 in A {
                print "+" $0 RS A[$1]
        }
' text.txt head.txt > outB.tmp

real	0m22.600s
user	0m19.482s
sys	0m3.078s

time awk 'FNR==NR {h[$1]=$2;next} $1 in h {print "+" $1, h[$1];print $2}' header.txt RS="+" text.txt > outC.tmp

real	1m29.579s
user	1m25.451s
sys	0m3.584s