Finding Duplicated Words in a Document

A common error when writing large amounts of prose is to accidentally duplicate words. Often you will see this in text as something like "the the program does the following ...." When the text is on-line, often the duplicated words occur at the end of one line and the beginning of another, making them very difficult to spot.

This program, `dupword.awk', scans through a file one line at a time, and looks for adjacent occurrences of the same word. It also saves the last word on a line (in the variable prev) for comparison with the first word on the next line.

The first two statements make sure that the line is all lower-case, so that, for example, "The" and "the" compare equal to each other. The second statement removes all non-alphanumeric and non-whitespace characters from the line, so that punctuation does not affect the comparison either. This sometimes leads to reports of duplicated words that really are different, but this is unusual.

# dupword --- find duplicate words in text
# Arnold Robbins, arnold@gnu.ai.mit.edu, Public Domain
# December 1991

{
    $0 = tolower($0)
    gsub(/[^A-Za-z0-9 \t]/, "");
    if ($1 == prev)
        printf("%s:%d: duplicate %s\n",
            FILENAME, FNR, $1)
    for (i = 2; i <= NF; i++)
        if ($i == $(i-1))
            printf("%s:%d: duplicate %s\n",
                FILENAME, FNR, $i)
    prev = $NF
}

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