awk - Remove line if field is duplicate

Question

Looking for an awk (or sed) one-liner to remove lines from the output if the first field is a duplicate.

An example for removing duplicate lines I've seen is:

awk 'a !~ $0; {a=$0}'

Tried using it for a basis with no luck (I thought changing the $0's to $1's would do the trick, but didn't seem to work).

Answer 1

$1 !~ /pattern/

Answer 2

awk '{ if (a[$1]++ == 0) print $0; }' "$@"

This is a standard (very simple) use for associative arrays.

Answer 3

this is how to remove duplicates

awk '!_[$1]++' file