第60页 | Learning the Bash Shell | 阅读 ‧ 电子书库

Textual Completion

Although the character-finding commands and | are not particularly useful, vi-mode provides one additional feature that we think you will use quite often: textual completion. This feature is not part of the real vi editor, and it was undoubtedly inspired by similar features in emacs and, originally, in the TOPS-20 operating system for DEC mainframes.

The rationale behind textual completion is simple: you should have to type only as much of a filename, user name, function, etc. as is necessary. Backslash (\) is the command that tells bash to do completion in vi-mode. If you type in a word, hit ESC to enter control mode, and then type \, one of four things will happen; they are the same as for TAB in emacs-mode:

 

If there is nothing whose name begins with the word, the shell will beep and nothing further will happen.If there is a command name in the search path, a function name, or a filename that the string uniquely matches, the shell will type the rest of it, followed by a space in case you want to type in more command arguments. Command name completion is only attempted when the word is in a command position (e.g., at the start of a line).If there is a directory that the string uniquely matches, the shell will complete the filename, followed by a slash.If there is more than one way to complete the name, the shell will complete out to the longest common prefix among the available choices. Commands in the search path and functions take precedence over filenames.

A related command is *. It behaves similarly to ESC-\, but if there is more than one completion possibility (number four in the previous list), it lists all of them and allows you to type further. Thus, it resembles the * shell wildcard character.

Less useful is the command =, which does the same kind of expansion as *, but in a different way. Instead of expanding the names onto the command line, it prints them, then gives you your shell prompt back and retypes whatever was on your command line before you typed =. For example, if the files in your directory include tweedledee.c and tweedledum.c, and you type tweedl followed by ESC and then =, you will see this:

$ cc tweedl
tweedledee.c tweedledum.c

It is also possible to expand other environment entities, as we saw in emacs-mode. If the text being expanded is preceded by a dollar sign ($), the shell will attempt to expand the name to that of a shell variable. If the text is preceded by a tilde (~), expansion to a username is attempted; if preceded by an at sign (@), a hostname.