Mac 上奇怪的 uniq 输出

Question

Here is the input file and output, I think characters like c and g should not be output?

$ uniq c.txt
a
g
b
g
c
v
c
$ cat c.txt
a
g
b
b
g
g
c
v
c

thanks in advance, Lin

Answer 1

From the uniq man page :

Repeated lines in the input will not be detected if they are not adjacent, so it may be necessary to sort the files first.

macbook:stackoverflow joeyoung$ cat c.txt
a
g
b
b
g
g
c
v
c
macbook:stackoverflow joeyoung$ uniq c.txt
a
g
b
g
c
v
c
macbook:stackoverflow joeyoung$ sort -u c.txt
a
b
c
g
v
macbook:stackoverflow joeyoung$ sort c.txt | uniq
a
b
c
g
v