bash on Mac OS X
Pages: 1, 2
A regular variable typically holds a piece of information that you use
frequently. Because variables in shell scripts are loosely typed, unlike
C and Java, variables
can hold virtually anything: a number, string, or composite value such
as an array or hash. Creating a variable is pretty painless:
and retrieving its value is almost as easy:
Thus, if you wished to see the current date when opening a new Terminal window, you could place the following lines in your profile:
mydate=`date "+%H:%M:%S %m/%d/%y"` echo "hi $USER, the current time is $mydate"
For more information on shell scripting, refer to Chris Stone's series of articles mentioned in the introduction.
Environment variables are essentially a special case of shell variables; they are visible to all child processes that are spawned from the shell. In layman's terms, this means that applications and scripts that are executed from within shell can read the value of the shell's environment variables; as a result, command-line tools typically use environment variables for configuration settings.
By convention, the names of environment variables are all uppercase. Environment variables on OS X may include the following:
|PATH||A list of colon-separated directories where the shell will look for executable files||/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin|
|CLASSPATH||A list of colon-separated directories and/or JAR files that contain Java class files that may be required in the Java Runtime Environment.||/Users/dave/FVL/Java/xerces.jar:
|JAVA_HOME||The root directory of your Java installation.||/Library/Java/Home|
|PWD||Your current directory in the file system.||/Applications|
|USER||Your login name.||dave|
To find out which environment variables have been defined in your shell,
env command, which simply echoes all the environment
variables to the terminal:
Figure 4: All environment variables defined in my shell.
Creating new environment variables is pretty simple; bash uses
export VAR_NAME=value. Thus any shell variable
can be turned into an environment variable via the
# create the JAVA_HOME environment variable export JAVA_HOME=/Library/Java/Home # do the same thing explicitly, using two lines JAVA_HOME=/Library/Java/Home export JAVA_HOME
And what happens if a required environment variable doesn't exist? Nothing too drastic -- the kernel won't panic and your computer won't start blowing smoke. It shouldn't, anyway. The shell and related tools require certain variables to be defined (such as ), but other tools may need their own environment variables. In the event that you are missing a required variable, chances are the related program will fail safely and let you know what needs to be defined, as does Apache's fop:
Figure 5: A typical example of missing an environment variable.
The following table lists the differences in working with variables (both shell and environment variables) between tcsh and bash on OS X:
|Display all shell variables||
|Create a shell variable||
|Remove a shell variable||
|List all environment variables||
|Create an environment variable||
|Remove an environment variable||
Aliases have been a part of Mac OS for several generations now. However, the terminology has gotten a bit confusing with Mac OS X since it's a branch between two traditionally distinct family trees: Unix and Mac OS, each with their own vocabulary. So it shouldn't be too much of a surprise that bringing the two together results in some conflict. One example of this is the term alias: the Finder and Unix underbelly each use the term for two different things:
- In the Finder, aliases make it convenient to access a file that is somewhere else on your hard drive; an alias essentially allows you to access the same file from multiple places.
- Aliases in shells serve a similar purpose, but because they exist
in a text-only environment, their role is a little different (the
Unix equivalent of the Finder's alias is called a
link); shell aliases allow you to remap virtually any Unix command to another name, and the aliased commands can then be invoked using their new name.
Aliases are declared in a similar method to variables, with the keyword
alias in front of the declaration:
If the command contains spaces, then you will have to wrap it in double
quotes. To find out which aliases you have already defined, simply enter
alias (in the event that you wish to remove
an alias, then you can simply use the command
alias l="ls -l" alias ll="ls -al" alias ~="cd ~" alias md=mkdir alias mckoi="java com.mckoi.runtime.McKoiDBMain " # remove the alias named md (for demonstration purposes) unalias md
The following image illustrates the use of the first two aliases created above:
Figure 6: An example of how even simple aliases can save you time at the keyboard.
Setting Your Prompt
After opening a Terminal window and being greeted by the message of the day, the first thing you'll see is your command prompt, waiting to accept your every wish. If you went ahead and changed your prompt in Jaguar with tcsh, chances are you'll be disappointed when you first see Panther's default prompt, which should appear something like:
Figure 7: The default prompt for bash in Panther.
Like tcsh, however, it is a relatively trivial process to change
your prompt in bash by setting the value of two special shell
PS2. Why two, you may ask?
Good question --
PS1 is can be considered to be the primary
prompt, which is displayed every time a new command can be
PS2 is the secondary prompt that is displayed
when a command spans more than one line. This screen shot illustrates
the two prompts in use:
Figure 8: An illustration of
in bash's default configuration.
The following table lists the information that you may wish to insert into your prompt:
|\a||ASCII bell character||--|
|\d||the current date||Sun Feb 08|
|\w||current working directory||/Applications/Network|
|\W||basename of the current working directory||Network|
|\T||current time (12-hour HH:MM:SS format)||01:16:49|
|\t||current time (HH:MM:SS format)||13:16:49|
|\@||current time (12-hour AM/PM format)||1:16 PM|
|\\||print a backslash||\|
From the information listed in the above table, we can see that Panther's default prompt strings are created using the following commands:
PS1="\h:\w \u$ " PS2=" > "
This article provides an overview on making the transition from tcsh and bash; at this point you should now know enough about bash to start tailoring your Panther environment to your needs. And while this article covers several key features of it, we have barely scratched the surface; command history, job control, scripting, and several other features went untouched. For more information, be sure to check out the following resources:
- As with most Unix programs, the bash documentation is installed
along with the program itself, and it can be found in the man pages.
Simply type the command
man bashat the prompt to read the pages.
- The Free Software Foundation's web site hosts the complete manual for the bash shell.
- Learning the bash Shell, 2nd Edition by Cameron Newham & Bill Rosenblatt (O'Reilly & Associates, 1998) provides an in-depth introduction to the basics of shells, and then goes on to cover everything you would ever need to know about bash.
David Miller is combining his passions of photography and working on the web at iStockphoto; when not hacking away with a text editor and a few web browsers in hand, he can be seen huddled over his laptop tweaking levels and curves for his freelance photography. Keep track of David's latest projects over at his home on the web.
Return to the Mac DevCenter
setting environment variable
2007-11-23 11:00:12 valentina84 [View]
2006-06-10 01:11:37 nitewing98 [View]
- Trackback from http://raible.org/archives/308-Mittwochmorgens-1900-in-Deutschland.html
Mittwochmorgens 19:00 in Deutschland
2004-10-06 09:59:39 [View]
- Trackback from http://www.heyotwell.com/heyblog/archives/2004/09/so_much_geeklin.html
So much geekliness
2004-09-06 11:36:30 [View]
2004-03-18 10:46:29 xyzzy-xyzzy [View]
- Trackback from http://www.zaneedwards.com/mt/mac/archives/000197.html
2004-02-28 07:15:11 [View]
2004-02-27 10:50:46 jeblanton [View]
Come to where the flavour is...
2004-02-25 16:11:51 pmccann [View]
- Trackback from http://www.afroginthevalley.com/hyperliens/archives/2004_02.html#000113
Bash sur OSX
2004-02-25 11:42:43 [View]
main question is..why use bash?
2004-02-25 09:52:06 pteeter [View]
if only ...
2004-02-25 08:09:07 henksmets [View]
if only ...
2004-02-25 08:54:46 blalor [View]
2004-02-25 00:07:11 housemaister [View]
2004-02-24 23:38:59 adpsk [View]
2004-02-24 19:12:52 keath [View]
bash on Mac OS X
2004-02-24 17:30:25 [View]