Classic Shell Scripting

Counting Lines, Words, and Characters

We have used the word-count utility, wc, a few times before. It is probably one of the oldest, and simplest, tools in the Unix toolbox, and POSIX standardizes it. By default, wc outputs a one-line report of the number of lines, words, and bytes:

$ echo This is a test of the emergency broadcast system | wc    
            Report counts
      1       9      49

Request a subset of those results with the -c (bytes), -l (lines), and -w (words) options:

$ echo Testing one two three | wc -c     
            Count bytes
22

$ echo Testing one two three | wc -l     
            Count lines
1

$ echo Testing one two three | wc -w     
            Count words
4

The -c option originally stood for character count, but with multibyte character-set encodings, such as UTF-8, in modern systems, bytes are no longer synonymous with characters, so POSIX introduced the -m option to count multibyte characters. For 8-bit character data, it is the same as -c.

Although wc is most commonly used with input from a pipeline, it also accepts command-line file arguments, producing a one-line report for each, followed by a summary report:

$ wc /etc/passwd /etc/group              
            Count data in two files
    26     68   1631 /etc/passwd
 10376  10376 160082 /etc/group
 10402  10444 161713 total

Modern versions of wc are locale-aware: set the environment variable LC_CTYPE to the desired locale to influence wc's interpretation of byte sequences as characters and word separators.

In Chapter 5, we will develop a related tool, wf, to report the frequency of occurrence of each word.