How to delete the matching pattern from given occu

Question

I'm trying to delete matching patterns, starting from the second occurrence, using sed or awk. The input file contains the information below:

abc
def
abc
ghi
jkl
abc
xyz
abc

I want to the delete the pattern abc from the second instance. The output should be as below:

abc
def
ghi
jkl
xyz

Answer 1

One way using awk:

$ awk 'f&&$0==p{next}$0==p{f=1}1' p="abc" file
abc
def
ghi
jkl
xyz

Just set p to pattern that you only want the first instance of printing:

Answer 2

Taken from : unix.com

Using awk '!x[$0]++' will remove duplicate lines. x is a array and it's initialized to 0.the index of x is $0,if $0 is first time meet,then plus 1 to the value of x[$0],x[$0] now is 1.As ++ here is "suffix ++",0 is returned and then be added.So !x[$0] is true,the $0 is printed by default.if $0 appears more than once,! x[$0] will be false so won't print $0.

Answer 3

$ awk '$0=="abc"{c[$0]++} c[$0]<2; ' file
abc
def
ghi
jkl
xyz

Just change the "2" to "3" or whatever number you want to keep the first N occurrences instead of just the first 1.

Answer 4

Neat sed solution:

sed '/abc/{2,$d}' test.txt
abc
def
ghi
jkl
xyz