打印唯一的行，比较不超过N个字符

Question

With uniq , you can choose to compare only first N characters

$ cat foo.txt
The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy cat.
The quick brown fox jumps over the lazy mouse.

$ uniq -w 40 foo.txt
The quick brown fox jumps over the lazy dog.

Can the same effect be achieved using awk ? I read this example

awk '!a[$0]++'

but it compares the whole line.

Answer 1

awk has substr() function:

awk '!a[substr($0,1,40)]++'

with your example:

kent$  echo "The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy cat.
The quick brown fox jumps over the lazy mouse."|awk '!a[substr($0,1,40)]++'
The quick brown fox jumps over the lazy dog

Answer 2

Two alternatives using FIELDWIDTHS and FPAT :

awk '!a[$1]++' FIELDWIDTHS=40

awk '!a[$1]++' FPAT='.{40}'