Question

Given input file

z
b
a
f
g
a
b
...

I want to output the number of occurrences of each string, for example:

z 1
b 2
a 2
f 1
g 1

How can this be done in a bash script?

Answer 1

You can sort the input and pass to uniq -c:

$ sort input_file | uniq -c
 2 a
 2 b
 1 f
 1 g
 1 z

If you want the numbers on the right, use awk to switch them:

$ sort input_file | uniq -c | awk '{print $2, $1}'
a 2
b 2
f 1
g 1
z 1

Alternatively, do the whole thing in awk:

$ awk '
{
    ++count[$1]
}
END {
    for (word in count) {
        print word, count[word]
    }
}
' input_file
f 1
g 1
z 1
a 2
b 2