Unix Power Tools, Third Edition chapter excerpt
By Shelley Powers, Jerry Peek, Tim O'Reilly, Mike Loukides



Saving Time on the Command Line

28.1. What’s Special About the Unix Command Line

One of Unix’s best features is the shell’s command line. Why? Nearly every modern operating system has a command line; we don’t use card readers with obscure job setup cards any more. What makes Unix’s special?The Unix shell command line of shortcuts. Some of these you’ll find in other operating systems; some you won’t. In this chapter, we’ll introduce a lot of these shortcuts. Among other things, we’ll discuss:

· How to run commands more than once (28.8).
· Filename completion (28.6, 28.7), which allows you to type the beginning of a filename and let the shell fill in the rest. (This is finally possible on certain Redmond-born OSes as well, but it usually involves a registry hack or two.)
· Command substitution (28.14), which lets you use the output from one command as arguments to another. (Note that this is different from pipelining.)
· Process substitution in bash, and a script named ! for other shells, lets you put the output of a command into a temporary file and give that filename to a process.
· The ability to repeat commands with various methods (28.10, 28.11).
· Handling of command lines that become too long (28.17).

Some fundamental command-line features that we aren’t discussing in this chapter, but which are discussed elsewhere, are:

· Job control (23.3), which lets you run several commands at the same time.
· Aliases (29.2), or abbreviations, for commands. Shell functions (29.11) are similar.
· Command-line editing (30.14) and history substitution (30.8). These are two different ways (both useful) to “recall” previous commands.
· Quoting (27.12, 27.13), the way you “protect” special characters from the Unix shell.
· Wildcards (33.2).

You don’t need to be a command-line virtuoso to use Unix effectively. But you’d be surprised at how much you can do with a few tricks. If all you can do at the command line is type ls or start Mozilla or the Gimp, you’re missing out on a lot.

--ML

28.2. Reprinting Your Command Line with CTRL-r

You’re logged in from home, running a program and answering a prompt. As you’re almost done, modem noise prints xDxD@! on your screen. Where were you? Or you’re typing a long command line and a friend interrupts you with write (1.21) to say it’s time for lunch. Do you have to press CTRL-u and start typing all over again?

If your system understands the rprnt character (usually set to CTRL-r), you can ask for the command line to be reprinted as it was. In fact, you can use CTRL-r any time you want to know what the system thinks you’ve typed on the current line—not just when you’re interrupted. But this only works in the normal cooked input mode; programs like vi that do their own input processing may treat CTRL-r differently. Here’s an example:

% egrep '(10394|29433|49401)' /work/symtower/

Message from alison@ruby on ttyp2 at 12:02 ...

how about lunch?
EOF
CTRL-r
egrep '(10394|29433|49401)' /work/symtower/logs/*

After the interruption, I just pressed CTRL-r. It reprinted the stuff I’d started typing. I finished typing and pressed RETURN to run it.

If you use a shell like the Korn shell that has interactive command editing, you can probably use it to reprint the command line, too. In bash and other commands that use the readline file, though, from vi editing mode, CTRL-r still seems to start an Emacs-style reverse search. So I added this fix to my ~/.inputrc file:

set editing-mode vi

# By default, in vi text-input mode, ^R does Emacs "reverse-i-search".
# In command mode, you can use the vi command ^L to redraw the line.
# Fix it in text-input mode:
"\\C-r": redraw-current-line

--JP

28.3. Use Wildcards to Create Files?

The shells’ [] (square bracket) wildcards will match a range of files. For instance, if you have files named afile, bfile, cfile, and dfile, you can print the first three by typing:

% lpr [a-c]file

Now, let’s say that you want to create some more files called efile, ffile, gfile, and hfile. What’s wrong with typing the command line below? Try it. Instead of vi, you can use your favorite editor or the touch (14.8) command:

% vi [e-h]file Doesn't make those four files
% ls
afile bfile cfile dfile

Stumped? Take a look at article 1.13 about wildcard matching.

The answer: wildcards can’t match names that don’t exist yet. That’s especially true with a command like touch ?file (14.8) or touch *file—think how many filenames those wildcards could possibly create!

Article 28.4 explains shell {_ } operators that solve this problem. And, by the way, if you just created one new file named [e-h]file, simply quote (27.12) its name to remove it:

rm "[e-h]file"

--JP