Shell command: uniq

Options

`-c`	`--count`		Prefix lines by the number of occurrences
`-d`	`--repeated`		Only print duplicate lines, one for each group. This option is very useful to determine if a text contains duplicated lines.
`-D`			Print all duplicate lines
	`--all-repeated`	`[=METHOD]`	Like `-D`, but allow separating groups with an empty line. `METHOD` is one of `none` (the default), `prepend` or `separate`
`-f`	`--skip-fields=`	`N`	Avoid comparing the first `N` fields
	`--group`	`[=METHOD]`	Show all items, separating groups with an empty line. `METHOD` is one of `separate` (the default), `prepend`, `append` or `both`
`-i`	`--ignore-case`		Ignore differences in case when comparing
`-s`	`--skip-chars=`	`N`	Avoid comparing the first `N` characters
`-u`	`--unique`		Only print unique lines
`-z`	`--zero-terminated`		Line delimiter is `NUL`, not line break
`-w`	`--check-chars=`	`N`	Compare no more than `N` characters in lines
	`--help`
	`--version`

The -d options allows to quickly determine if a file contains duplicated lines.

The following pipeline prints nothing:

echo 'This
text
does
not
have
duplicates' | sort | uniq -d

This pipeline prints the word this because it is duplicated:

echo 'in
this
text,
the
word
this
occurs
twice' | sort | uniq -d

The following pipeline counts how many git commits each author has contributed to a git repository:

$ git log --format='%aN' | sort | uniq -c  | sort -nr

uniq does not detect repeated lines unless they are adjacent.

Try using sort -u (without uniq).