Sort and count number of occurrence of lines

| sort | uniq -c

As stated in the comments.

Piping the output into sort organises the output into alphabetical/numerical order.

This is a requirement because uniq only matches on repeated lines, ie

a
b
a

If you use uniq on this text file, it will return the following:

a
b
a

This is because the two as are separated by the b - they are not consecutive lines. However if you first sort the data into alphabetical order first like

a
a
b

Then uniq will remove the repeating lines. The -c option of uniq counts the number of duplicates and provides output in the form:

2 a
1 b

References:

• sort(1)
• uniq(1)

[your command] | sort | uniq -c | sort -nr

The accepted answer is almost complete you might want to add an extra sort -nr at the end to sort the results with the lines that occur most often first

uniq options:

-c, --count
       prefix lines by the number of occurrences

sort options:

-n, --numeric-sort
       compare according to string numerical value
-r, --reverse
       reverse the result of comparisons

In the particular case were the lines you are sorting are numbers, you need use sort -gr instead of sort -nr, see comment

You can use an associative array on awk and then -optionally- sort:

$ awk ' { tot[$0]++ } END { for (i in tot) print tot[i],i } ' access.log | sort

output:

1 c.php
1 d.php
2 b.php
3 a.php