Classic Shell Scripting

Chapter 12. Spellchecking

This chapter uses the task of spellchecking to demonstrate several different dimensions of shell scripting. After introducing the spell program, we show how a simple but useful spellchecker can be constructed almost entirely out of stock Unix tools. We then proceed to show how simple shell scripts can be used to modify the output of two freely available spellchecking programs to produce results similar to those of the traditional Unix spell program. Finally, we present a powerful spellchecker written in awk, which nicely demonstrates the elegance of that language.

The spell Program

The spell program does what you think it does: it checks a file for spelling errors. It reads through all the files named on the command line, producing, on standard output, a sorted list of words that are not in its dictionary or that cannot be derived from such words by the application of standard English grammatical rules (e.g., "words" from "word"). Interestingly enough, POSIX does not standardize spell. The Rationale document has this to say:

This utility is not useful from shell scripts or typical application programs. The spell utility was considered, but was omitted because there is no known technology that can be used to make it recognize general language for user-specified input without providing a complete dictionary along with the input file.

We disagree with the first part of this statement. Consider a script for automated bug or trouble reporting: one might well ...