$ cat file
filed1 filed2 field3_1 field4
filed1 filed2 field3_2 field4
filed1 filed2 field3_3 field4
filed1 filed2 field3_4 field4
filed1 filed2 field3_5 field4
filed1 filed2 field3_6 field4
filed1 filed2 field3_7 field4
$ a=($(cut -d" " -f3 file))
$ i=0;until((i>=(${#a}-1)));do echo ${a[i]};((i+=1));done
field3_1
field3_2
field3_3
field3_4
field3_5
field3_6
field3_7

awk '{x[NR]=$3}
END{for(i=1;i<=NR;i++)print x[i]}' file