It’s always possible to make mistakes when you type at a computer keyboard, but perhaps even more so when you are using a Unix shell. Unix shell syntax is powerful, yet terse, full of odd characters, and not particularly mnemonic, making it possible to construct command lines that are as cryptic as they are complex. The Bourne and C shells exacerbate this situation by giving you extremely limited ways of editing your command lines.
In particular, there is no way to recall a previous command line so that you can fix a mistake. For example, in Chapter 7 we’ll see complex command lines like:
eval cat \$srcname \| ccom \| optimize \| as \> \$objname
If you are an experienced Bourne shell user, undoubtedly you know the frustration of having to retype lines like this. You can use the backspace key to edit, but once you hit ENTER, it’s gone forever!
The C shell provides a small improvement via its history mechanism, which provides a few very awkward ways of editing previous commands. But there are more than a few people who have wondered, “Why can’t I edit my Unix command lines in the same way I can edit text with an editor?”
This is exactly what the Korn shell allows you to do. It has editing modes that allow you to edit command lines with editing commands similar to those of the two most popular Unix editors, vi and Emacs. It also provides a much-extended analogue to the C shell history mechanism called hist (for “history”) that, among ...