Node:Wc Program, Previous:Uniq Program, Up:Clones

Counting Things

The wc (word count) utility counts lines, words, and characters in one or more input files. Its usage is as follows:

wc [-lwc] [ files ... ]

If no files are specified on the command line, wc reads its standard input. If there are multiple files, it also prints total counts for all the files. The options and their meanings are shown in the following list:

-l

Count only lines.

-w

Count only words. A "word" is a contiguous sequence of nonwhitespace characters, separated by spaces and/or tabs. Luckily, this is the normal way awk separates fields in its input data.

-c

Count only characters.

Implementing wc in awk is particularly elegant, since awk does a lot of the work for us; it splits lines into words (i.e., fields) and counts them, it counts lines (i.e., records), and it can easily tell us how long a line is.

This uses the getopt library function (see Processing Command-Line Options) and the file-transition functions (see Noting Data File Boundaries).

This version has one notable difference from traditional versions of wc: it always prints the counts in the order lines, words, and characters. Traditional versions note the order of the -l, -w, and -c options on the command line, and print the counts in that order.

The BEGIN rule does the argument processing. The variable print_total is true if more than one file is named on the command line:

# wc.awk --- count lines, words, characters

# Options:
#    -l    only count lines
#    -w    only count words
#    -c    only count characters
#
# Default is to count lines, words, characters
#
# Requires getopt and file transition library functions

BEGIN {
    # let getopt print a message about
    # invalid options. we ignore them
    while ((c = getopt(ARGC, ARGV, "lwc")) != -1) {
        if (c == "l")
            do_lines = 1
        else if (c == "w")
            do_words = 1
        else if (c == "c")
            do_chars = 1
    }
    for (i = 1; i < Optind; i++)
        ARGV[i] = ""

    # if no options, do all
    if (! do_lines && ! do_words && ! do_chars)
        do_lines = do_words = do_chars = 1

    print_total = (ARGC - i > 2)
}

The beginfile function is simple; it just resets the counts of lines, words, and characters to zero, and saves the current file name in fname:

function beginfile(file)
{
    chars = lines = words = 0
    fname = FILENAME
}

The endfile function adds the current file's numbers to the running totals of lines, words, and characters.¹ It then prints out those numbers for the file that was just read. It relies on beginfile to reset the numbers for the following data file:

function endfile(file)
{
    tchars += chars
    tlines += lines
    twords += words
    if (do_lines)
        printf "\t%d", lines
    if (do_words)
        printf "\t%d", words
    if (do_chars)
        printf "\t%d", chars
    printf "\t%s\n", fname
}

There is one rule that is executed for each line. It adds the length of the record, plus one, to chars. Adding one plus the record length is needed because the newline character separating records (the value of RS) is not part of the record itself, and thus not included in its length. Next, lines is incremented for each line read, and words is incremented by the value of NF, which is the number of "words" on this line:

# do per line
{
    chars += length($0) + 1    # get newline
    lines++
    words += NF
}

Finally, the END rule simply prints the totals for all the files:

END {
    if (print_total) {
        if (do_lines)
            printf "\t%d", tlines
        if (do_words)
            printf "\t%d", twords
        if (do_chars)
            printf "\t%d", tchars
        print "\ttotal"
    }
}

Footnotes

1. wc can't just use the value of FNR in endfile. If you examine the code in Noting Data File Boundaries you will see that FNR has already been reset by the time endfile is called.