How does this awk script to delete blank and duplicate lines work?
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This awk command is used to delete blank and duplicate lines:
sort abc.log | awk 'LAST != $0 print LAST=$0'
I'd like to know how "LAST != $0" and "LAST=$0" are used and what do they do?
awk
edited Jan 18 at 14:51
Mr Shunz
3,47712127
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
add a comment |
This awk command is used to delete blank and duplicate lines:
sort abc.log | awk 'LAST != $0 print LAST=$0'
I'd like to know how "LAST != $0" and "LAST=$0" are used and what do they do?
awk
edited Jan 18 at 14:51
Mr Shunz
3,47712127
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
I has add exact need, and the confusion has been solved.
– wang xiaoshi
Jan 18 at 8:18
add a comment |
This awk command is used to delete blank and duplicate lines:
sort abc.log | awk 'LAST != $0 print LAST=$0'
I'd like to know how "LAST != $0" and "LAST=$0" are used and what do they do?
awk
edited Jan 18 at 14:51
Mr Shunz
3,47712127
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
This awk command is used to delete blank and duplicate lines:
sort abc.log | awk 'LAST != $0 print LAST=$0'
I'd like to know how "LAST != $0" and "LAST=$0" are used and what do they do?
awk
awk
edited Jan 18 at 14:51
Mr Shunz
3,47712127
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
edited Jan 18 at 14:51
Mr Shunz
3,47712127
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
edited Jan 18 at 14:51
Mr Shunz
3,47712127
edited Jan 18 at 14:51
Mr Shunz
3,47712127
edited Jan 18 at 14:51
Mr Shunz
3,47712127
3,47712127
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
asked Jan 16 at 2:52
wang xiaoshiwang xiaoshi
61
61
I has add exact need, and the confusion has been solved.
– wang xiaoshi
Jan 18 at 8:18
add a comment |
I has add exact need, and the confusion has been solved.
– wang xiaoshi
Jan 18 at 8:18
I has add exact need, and the confusion has been solved.
– wang xiaoshi
Jan 18 at 8:18
I has add exact need, and the confusion has been solved.
– wang xiaoshi
Jan 18 at 8:18
add a comment |
1 Answer
1
active
oldest
votes
The sort command sorts the lines of abc.log. The result is that duplicate lines follow each other.
awk take this sorted file as input. It compares the current line (which is in $0) with the content of the variable LAST. Only if it is different (!=), the line is printed. The content of the current line is than stored in the variable LAST. So it can be compared in the next iteration.
NB: Instead of using this combination of sort and awk, just use sort -u abc.log to remove duplicate lines.
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
2
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (whichsortputs first), butsort -udoes not, althoughsort -u | grep .does.
– dave_thompson_085
Jan 16 at 6:26
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
Indeed, if the input includes empty lines and yousort -rand pipe to thatawk, you get an empty line at the end of the output. If you justsort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.
– fra-san
Jan 18 at 15:04
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The sort command sorts the lines of abc.log. The result is that duplicate lines follow each other.
awk take this sorted file as input. It compares the current line (which is in $0) with the content of the variable LAST. Only if it is different (!=), the line is printed. The content of the current line is than stored in the variable LAST. So it can be compared in the next iteration.
NB: Instead of using this combination of sort and awk, just use sort -u abc.log to remove duplicate lines.
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
2
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (whichsortputs first), butsort -udoes not, althoughsort -u | grep .does.
– dave_thompson_085
Jan 16 at 6:26
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
Indeed, if the input includes empty lines and yousort -rand pipe to thatawk, you get an empty line at the end of the output. If you justsort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.
– fra-san
Jan 18 at 15:04
add a comment |
The sort command sorts the lines of abc.log. The result is that duplicate lines follow each other.
awk take this sorted file as input. It compares the current line (which is in $0) with the content of the variable LAST. Only if it is different (!=), the line is printed. The content of the current line is than stored in the variable LAST. So it can be compared in the next iteration.
NB: Instead of using this combination of sort and awk, just use sort -u abc.log to remove duplicate lines.
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
2
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (whichsortputs first), butsort -udoes not, althoughsort -u | grep .does.
– dave_thompson_085
Jan 16 at 6:26
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
Indeed, if the input includes empty lines and yousort -rand pipe to thatawk, you get an empty line at the end of the output. If you justsort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.
– fra-san
Jan 18 at 15:04
add a comment |
The sort command sorts the lines of abc.log. The result is that duplicate lines follow each other.
awk take this sorted file as input. It compares the current line (which is in $0) with the content of the variable LAST. Only if it is different (!=), the line is printed. The content of the current line is than stored in the variable LAST. So it can be compared in the next iteration.
NB: Instead of using this combination of sort and awk, just use sort -u abc.log to remove duplicate lines.
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
The sort command sorts the lines of abc.log. The result is that duplicate lines follow each other.
awk take this sorted file as input. It compares the current line (which is in $0) with the content of the variable LAST. Only if it is different (!=), the line is printed. The content of the current line is than stored in the variable LAST. So it can be compared in the next iteration.
NB: Instead of using this combination of sort and awk, just use sort -u abc.log to remove duplicate lines.
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
answered Jan 16 at 5:59
finswimmerfinswimmer
3596
3596
2
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (whichsortputs first), butsort -udoes not, althoughsort -u | grep .does.
– dave_thompson_085
Jan 16 at 6:26
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
Indeed, if the input includes empty lines and yousort -rand pipe to thatawk, you get an empty line at the end of the output. If you justsort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.
– fra-san
Jan 18 at 15:04
add a comment |
2
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (whichsortputs first), butsort -udoes not, althoughsort -u | grep .does.
– dave_thompson_085
Jan 16 at 6:26
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
Indeed, if the input includes empty lines and yousort -rand pipe to thatawk, you get an empty line at the end of the output. If you justsort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.
– fra-san
Jan 18 at 15:04
2
2
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (which
sort puts first), but sort -u does not, although sort -u | grep . does.– dave_thompson_085
Jan 16 at 6:26
One small difference, alluded to in the Q: since awk vars are initialized to the empty string (also treated as numeric zero), the awk also deletes any empty lines (which
sort puts first), but sort -u does not, although sort -u | grep . does.– dave_thompson_085
Jan 16 at 6:26
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
thank you! this can explain how awk to delete duplicate records.
– wang xiaoshi
Jan 16 at 6:58
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
This solved my confusion.
– wang xiaoshi
Jan 18 at 8:13
Indeed, if the input includes empty lines and you
sort -r and pipe to that awk, you get an empty line at the end of the output. If you just sort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.– fra-san
Jan 18 at 15:04
Indeed, if the input includes empty lines and you
sort -r and pipe to that awk, you get an empty line at the end of the output. If you just sort, you don't. It is probably worth editing your answer, adding the information from dave_thompson_085's comment.– fra-san
Jan 18 at 15:04
add a comment |
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I has add exact need, and the confusion has been solved.
– wang xiaoshi
Jan 18 at 8:18