Filters and Regular Expressions (39)

The uniq command by default removes all but one copy of adjacent identical lines.

Some options:

`-c`		also print number of times each line is duplicated
`-d`		only print (one copy of) duplicated lines
`-u`		only print lines that occur uniquely (once only)

Surprisingly useful tool for summarising data, typically after extraction by cut. Always preceded by sort (why?).

# extract first field, sort, and tally
cut -f1 data  |  sort  |  uniq -c