Shell Programming and Scripting

chr5    118464905    118465027    ENST00000514151    utr5    0    +
chr5    118464903    118465118    ENST00000504031    utr5    0    +
chr5    118468826    118469180    ENST00000504031    utr5    0    +
chr5    118469920    118470084    ENST00000512281    utr5    0    +
chr5    118479535    118479625    ENST00000512281    utr5    0    +
chr5    118480230    118480333    ENST00000512281    utr5    0    +

ENST00000512281    Xkr4
ENST00000504031    Nku23
ENST00000776348    KKM2

chr5    118464903    118465118    ENST00000504031    utr5    0    +   Nku23
chr5    118468826    118469180    ENST00000504031    utr5    0    +   Nku23
chr5    118469920    118470084    ENST00000512281    utr5    0    +   Xkr4
chr5    118479535    118479625    ENST00000512281    utr5    0    +   Xkr4
chr5    118480230    118480333    ENST00000512281    utr5    0    +   Xkr4

awk 'NR==FNR{a[$1]=$2;next}a[$4]{print $0"\t"a[$4]}' file2 file1

awk 'NR==FNR{a[$1]=$2;next}a[$4]{$0=$0"\t"a[$4]}1' file2 file1

while read key value
do
  sed -i "/${key}/ s/$/ ${value}/" file1
done < file2

awk 'NF==8' file1

nawk 'NR==FNR { 
_[$1]=$2 
}
NR!=FNR {
  if(_[$4] != "")
    print $0"  "_[$4]
}' f2 f1