Running Linux, 5th Edition - Matthias Kalle Dalheimer [87]
A similar change exists with the while loop. In bash, this takes the following form:
while list
do
commands
done
You can negate the effect by replacing the word while with until. Again, list is just a command sequence to be executed, and the exit status determines the result (zero for success and nonzero for failure). Under tcsh the loop looks like this:
while (expression)
commands
end
where expression is a logical expression to be evaluated within tcsh.
This example should be enough to get a head start on understanding the overall differences of shell scripts under bash and tcsh. We encourage you to read the bash(1) and tcsh(1) manual pages (although they serve more as a reference than a tutorial) and Info pages, if you have them available. Various books and tutorials on using these two shells are available as well; in fact, any book on shell programming will do, and you can interpolate the advanced features of bash and tcsh into the standard Bourne and C shells using the manual pages. Learning the bash Shell by Cameron Newham and Bill Rosenblatt and Using csh and tcsh by Paul DuBois (both from O'Reilly) are also good investments.
Being More Efficient with the Z Shell
The Z shell (zsh) is particularly appreciated for its many features that make you more efficient on the command line. To start with, zsh does not have one command prompt, but rather two: one for the lefthand side, and one for the righthand side. The lefthand one is set as usual by assigning to the environment variable PROMPT; for the righthand side, the environment variable RPROMPT is used. For example:
export PROMPT="%n@%m"
export RPROMPT="%~%"
gives you your username and hostname to the left of the entry line, and the current directory to the right. The smart thing about the right prompt is that it disappears when you "need the space"; that is, it gets out of the way when your typing comes close.
An interesting thing about zsh is the many, many options that you can set with the setopt command. The manual page zshoptions will list all of them, but we'd like to mention at least one very useful one here, the ALL_EXPORT option. By specifying:
setopt ALL_EXPORT
any environment variable that you set will automatically be exported. This is very useful if you, like us, keep setting environment variables for processes other than the shell and then forget to export them, and wonder why they are not picked up by the processes started from the shell. You can turn this off with setopt noALL_EXPORT.
You have already seen how to use the cd command. Of course, zsh knows about cd as well, but it does some other interesting stuff. For example, if you specify -- (a dash) as the argument, you will be returned to the working directory that was your working directory before the last cd command (for the following example, we have moved the display of the current directory back to the lefthand side):
~%> cd kdesvn/kdelibs/kdecore
~/kdesvn/kdelibs/kdecore> pwd
/home/kalle/kdesvn/kdelibs/kdecore
~/kdesvn/kdelibs/kdecore> cd /usr/local
/usr/local> cd -
~/kdesvn/kdelibs/kdecore
~/kdesvn/kdelibs/kdecore>
Also, if you type in a command that zsh does not recognize (i.e., it is neither an executable in your PATH nor a built-in command), but there is a directory with the name of that command, zsh will interpret that as a request to change the working directory to that directory:
~> Documents
~/Documents>
Another neat feature is the autocorrection of commands. If you, like us, keep typing mroe instead of more, turn on the autocorrection by issuing:
setopt CORRECT
Now zsh will come up with suggestions if it cannot understand your command:
~/Documents> mroe /etc/motd
zsh: correct 'mroe' to 'more' [nyae]? y
Welcome to tigger...
Even when it comes to completion, zsh has a number of features that sets it apart from other shells. There are few things that it does not attempt completion on.