Counting characters with unix utilities

[John T Ellis]

In article <4002 at umbc3.UMBC.EDU> rouben at math9.math.umbc.edu () writes:
>How can I count the number of occurrences of a given character in a file?
>It can be done rather trivially in C, but I wonder if it can also be done
>using standard unix utilities like awk, sed, tr, wc, etc.
>
>The closest  I have come to this is the following construction:
>
>cat file | tr -c 'A' '' | wc -c
>
>which attempts to count the number of occurrences of the character "A"
>in the file.  The "tr" command replaced all characters different from
>"A" by the null character, then "wc" counts all characterters in its input
>(unfortunately) also counting the null characters :-(
[Text Deleted]

Try the following:

 cat file | tr -cs A-Za-z A-Za-z'\012' | sort | unique -c

If I understand tr, which is not necessarily true at this ungodly hour
of the morning :-), this should take the first occurence of either
A-Z or a-z and map it to A-Z or a-z with a line feed.  Hence, you get 
a long list with single characters.  Sort it and push it through
the unique filter which with the -c option tells you the number
of times a character appeared.

Note: This will differentiate between A and a.

John
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