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Hello
UnixPro Readers,
Of
all the books published on Unix over the past several
years one of the most ubiquitous is O'Reilly's Unix
Power Tools. It's a stunningly useful book that answers
those little nagging questions on how to perform tasks
in easier, more efficient ways. If your second or first
edition of Unix Power Tools is looking a little ragged,
you'll be happy to hear that the third edition was just
released in October. For your perusal, we offer Chapter
28 in today's UnixProNews. If you pick up a few handy
tips from this article, remember - the full book contains
a whopping 51 chapters. Finish it and you'll attain
guru status!
Saving
Time on the Command Line
Chapter excerpt from Unix Power Tools
By
Shelley Powers, Jerry Peek, Tim O'Reilly, Mike Loukides,
et. al.
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).
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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.
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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.
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In fact, you can use CTRL-r any time you want to know
what the
systemthinks 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 28.4. Build Strings with
{ } I’ve been finding
more and more uses for the {} pattern-expansion characters
in csh, tcsh, zsh, and bash. They’re similar to
*, ?, and [ ] (33.2), but they don’t match filenames
the way that *, ?, and [ ] do. You can give them arbitrary
text (not just filenames) to expand—that “expand-anything”
ability is what makes them so useful.
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