From 5a12e7c134274dba706667107d10d231517d3e05 Mon Sep 17 00:00:00 2001 From: Patrick J Volkerding Date: Wed, 26 Aug 2009 10:00:38 -0500 Subject: Slackware 13.0 Wed Aug 26 10:00:38 CDT 2009 Slackware 13.0 x86_64 is released as stable! Thanks to everyone who helped make this release possible -- see the RELEASE_NOTES for the credits. The ISOs are off to the replicator. This time it will be a 6 CD-ROM 32-bit set and a dual-sided 32-bit/64-bit x86/x86_64 DVD. We're taking pre-orders now at store.slackware.com. Please consider picking up a copy to help support the project. Once again, thanks to the entire Slackware community for all the help testing and fixing things and offering suggestions during this development cycle. As always, have fun and enjoy! -P. --- slackbook/html/shell-bash.html | 234 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 234 insertions(+) create mode 100644 slackbook/html/shell-bash.html (limited to 'slackbook/html/shell-bash.html') diff --git a/slackbook/html/shell-bash.html b/slackbook/html/shell-bash.html new file mode 100644 index 000000000..13ffdf089 --- /dev/null +++ b/slackbook/html/shell-bash.html @@ -0,0 +1,234 @@ + + + + +The Bourne Again Shell (bash) + + + + + + + + + +
+ + + + + + + + + + +
Slackware Linux Essentials
PrevChapter 8 The ShellNext
+ +
+
+ +
+

8.3 The Bourne Again Shell +(bash)

+ +
+

8.3.1 +Environment Variables

+ +

A Linux system is a complex beast, and there's a lot to keep track of, a lot of little +details that come into play in your normal interactions with various programs (some of +which you might not even need to be aware of). Nobody wants to pass a bunch of options to +every program that gets run, telling it what kind of terminal is being used, the hostname +of the computer, how their prompt should look...

+ +

So as a coping mechanism, users have what's called an environment. The environment +defines the conditions in which programs run, and some of this definition is variable; +the user can alter and play with it, as is only right in a Linux system. Pretty much any +shell will have environment variables (if not, it's probably not a very useable shell). +Here we will give an overview of the commands bash provides for manipulating its +environment variables.

+ +

set by itself will show you all of the environment variables +that are currently defined, as well as their values. Like most bash built-ins, it can also do several other things (with +parameters); we'll leave it to the bash(1) man page to cover +that, though. Example 8-1 shows +an excerpt from a set command run on one of the author's +computers. Notice in this example the PATH variable that was +discussed earlier. Programs in any of those directories can be run simply by typing the +base filename.

+ +
+

Example 8-1. Listing Environment Variables with set

+ + + + + +
+
+% set
+PATH=/usr/local/lib/qt/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:
+/usr/openwin/bin:/usr/games:.:/usr/local/ssh2/bin:/usr/local/ssh1/bin:
+/usr/share/texmf/bin:/usr/local/sbin:/usr/sbin:/home/logan/bin
+PIPESTATUS=([0]="0")
+PPID=4978
+PS1='\h:\w\$ '
+PS2='> '
+PS4='+ '
+PWD=/home/logan
+QTDIR=/usr/local/lib/qt
+REMOTEHOST=ninja.tdn
+SHELL=/bin/bash
+
+
+
+ + + + + +
+
+% unset VARIABLE
+
+
+ +

unset will remove any variables that you give it, wiping out +both the variable and its value; bash will forget that variable +ever existed. (Don't worry. Unless it's something you explicitly defined in that shell +session, it'll probably get redefined in any other session.)

+ + + + + +
+
+% export VARIABLE=some_value
+
+
+ +

Now, export is truly handy. Using it, you give the +environment variable VARIABLE the value “some_value”; if VARIABLE didn't exist, +it does now. If VARIABLE already had a value, well, it's gone. +That's not so good, if you're just trying to add a directory to your PATH. In that case, you probably want to do something like this:

+ + + + + +
+
+% export PATH=$PATH:/some/new/directory
+
+
+ +

Note the use of $PATH there: when you want bash to interpret a variable (replace it with its value), tack a +$ onto the beginning of the variable's name. For instance, echo $PATH will echo the value of PATH, in my +case:

+ + + + + +
+
+% echo $PATH
+/usr/local/lib/qt/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:
+/usr/openwin/bin:/usr/games:.:/usr/local/ssh2/bin:/usr/local/ssh1/bin:
+/usr/share/texmf/bin:/usr/local/sbin:/usr/sbin:/home/logan/bin
+
+
+
+ +
+

8.3.2 Tab +Completion

+ +

(Here comes something cool again.)

+ +
    +
  1. +

    A commandline interface means lots of typing.

    +
    2. + +
  2. +

    Typing is work.

    +
    3. + +
  3. +

    Nobody likes work.

    +
    4. +
+ +

From 3 and 2, we can determine that (4) nobody likes typing. Fortunately, bash saves us from (5) (nobody likes a commandline interface).

+ +

How does bash accomplish this wonderful feat, you ask? In +addition to the wildcard expansion we discussed before, bash +features tab completion.

+ +

Tab completion works something like this: You're typing the name of a file. Maybe it's +in your PATH, maybe you're typing it out explicitly. All you have +to do is type enough of the filename to uniquely identify it. Then hit the tab key. bash will figure out what you want and finish typing it for you!

+ +

Example time. /usr/src contains two subdirectories: /usr/src/linux and /usr/src/sendmail. I +want to see what's in /usr/src/linux. So I just type ls /usr/src/l, hit the TAB key, and bash gives me ls /usr/src/linux.

+ +

Now, suppose there are two directories /usr/src/linux and +/usr/src/linux-old; If I type /usr/src/l and hit TAB, bash will fill in as much as it can, and I'll get /usr/src/linux. I can stop there, or I can hit TAB again, and bash will show a list of +directories that match what I've typed so far.

+ +

Hence, less typing (and hence, people can like commandline interfaces). I told you it +was cool.

+
+
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+ + + + + + + + + + + + +
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