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deleting multiple accourances of a pattern from a file

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# 1  
Old 04-21-2009
deleting multiple accourances of a pattern from a file
I have a .sh file with the following contents:
a
b
c
a
a
b
d
c

i want to delete the multiple occurances and keep one. say there are 3 a's in the file. I want to delete 2 of them and just keep 1 occurance.
# 2  
Old 04-21-2009
sort -u a.sh


cheers,
Devaraj Takhellambam
# 3  
Old 04-21-2009
thanks Smilie
# 4  
Old 04-21-2009
Code:
nawk '!a[$0]++' a.sh

# 5  
Old 04-21-2009
if the file is like

a
c
b
check interface a
check interface b

and i want to perform the same action for both a and check interface a , thus i need to keep only one of them in my file. how do i do a sort in that case
# 6  
Old 04-21-2009
u need to understand the patter that precedes the text and remove it.

sed 's/check interface //g' dupsed | sort -u

cheers,
Devaraj Takhellambam
# 7  
Old 04-21-2009
can u expalin alitlle about dupsed. what does it do
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