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Top Forums UNIX for Dummies Questions & Answers fix the if and then error in bash Post 302566604 by Corona688 on Thursday 20th of October 2011 04:39:58 PM
Old 10-20-2011
Look at this line. What do you think it does?
Code:
http_proxy="hostname:3128" wget http://somesite.com/

It temporarily exports the http_proxy environment variable, setting it to hostname:3128, before running wget to retrieve a webpage. wget sees this variable and uses this proxy. Nothing else in the script sees the http_proxy variable change. It's a very handy ability considering how so many programs use environment vars like these.

You can also do
Code:
http_proxy= wget http://sometime.com/

to prevent wget from seeing an http_proxy something else exported globally. A shell which allowed spaces after the = wouldn't ever be able to do this.

You might have heard of an attempt at creating a 'better shell' with a less shell-like syntax, called the C shell. It's one of the worst shells there is because of its poorly chosen syntax which was built on convenience, leaving many inconsistent parts, parsing bugs that are impossible to fix, and many basic features which the syntax didn't leave any way to add.

There really is a reason the shell does a lot of things the way it does.

Last edited by Corona688; 10-20-2011 at 05:47 PM..
 

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SYSLOGOUT(8)						      System Manager's Manual						      SYSLOGOUT(8)

NAME
syslogout - modular centralized shell logout mechanism DESCRIPTION
syslogout is a generic approach to enable centralized shell logout actions for all users of a given system in a modular and centralized way mostly aimed at avoiding work for lazy sysadmins. It has only been tested to work with the bash shell. It basically consists of the small /etc/syslogout shell script which invokes other small shell scripts having a .bash suffix which are con- tained in the /etc/syslogout.d/ directory. The system administrator can drop in any script he wants without any naming convention other than that the scripts need to have a .bash suffix to enable automagic sourcing by the /etc/syslogout script. For shell sessions, the contents of /etc/syslogout.d/" will be sourced by every user at logout if the following lines are present in his $HOME/.bash_logout: if [ -f /etc/syslogout ]; then . /etc/syslogout fi If used for X sessions it is advisable to include the former statement into the Xreset script of the X display manager instead to prevent that closing of an terminal emulator window yields unexpected results in your running X session if your X11 terminal emulator is using a login shell. Be sure then to run it under the user-id of the X session's user. See the example files in /usr/share/doc/syslogout/ for illustration. Users not wanting /etc/syslogout to be sourced for their environment can easily disable it's automatic mechanism. It can be disabled by simply creating an empty file called $HOME/.nosyslogout in the user's home directory using e.g. the touch(1) command. Any single configuration file in /etc/syslogout.d/ can simply be overridden by any user by creating a private $HOME/.syslogout.d/ directory which may contain a user's own version of any configuration file to be sourced instead of the system default. It's names have just to match exactly the system's default /etc/syslogout.d/ configuration files. Empty versions of these files contained in the $HOME/.syslo- gout.d/ directory automatically disable sourcing of the system wide version. Naturally, users can add and include their own private scripts to be automagically executed by /etc/syslogout at logout time. OPTIONS
There are no options other than those dictated by shell conventions. Anything is defined within the configuration scripts themselves. SEE ALSO
The README files and configuration examples contained in /usr/share/doc/syslogout/ and the manual page for bash(1), xdm(1x), xdm.options(5), and wdm(1x). Recommended further reading is everything related with shell programming. If you need a similar mechanism for executing code at login time check out the related package sysprofile(8) which is a very close compan- ion to syslogout. BUGS
syslogout in its current form is mainly restricted to bash(1) syntax. In fact it is actually a rather embarrassing quick and dirty hack than anything else - but it works. It serves the practical need to enable a centralized bash configuration until something better becomes available. Your constructive criticism in making this into something better" is very welcome. Before i forget to mention it: we take patches... ;-) AUTHOR
syslogout was developed by Paul Seelig <pseelig@debian.org> specifically for the Debian GNU/Linux system. Feel free to port it to and use it anywhere else under the conditions of either the GNU public license or the BSD license or both. Better yet, please help to make it into something more worthwhile than it currently is. SYSLOGOUT(8)
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