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Top Forums Shell Programming and Scripting In bash, read to a variable with a default value to edit Post 302311449 by Mr.Lauren on Tuesday 28th of April 2009 05:14:23 PM
Old 04-28-2009
Method of real-time editing of variables in Bash

I realize this is an old post, but since I was so frustrated when I was trying to figure out how to do this, I thought it might be valuable to someone else to see this answer to the problem.

This may be pretty ugly to sophisticated programmers. I'm very "wet behind the ears" in Bash, or anything else for that matter. By the way, this is done in a Debian etch environment.

The idea is to save the variable to a file, and then open the file with an editor, make the desired changes, save the result, and exit the editor.

There must be some shell gymnastics going on here that I don't understand, because until I specified the whole path (with pwd), the edit did not take place.

If you want the new variable to exist as a permanent part of your script, you'll have to figure that out yourself. In my (DAR backup) program, I'm saving my editable variables to external files.

Here's my example script. The variable begins with 3 errors to be edited. So you can test it 3 times before you get it right. At the end the temporary file is deleted, because by that time you will have placed the variable where you want it.:

Code:
#!/bin/bash

## To test the editing of a variable from inside a script
if [ -f `pwd`/editvarfile.txt ] ; then echo "" ; else echo "This is a variible ti be editied." > `pwd`/editvarfile.txt ; fi
editvar=$(cat editvarfile.txt)
pickans="n"
while [ "$pickans" = "n" ] ; do
echo -n "The present variable is "$editvar".  Is this correct?  (y/n) "
read pickans
if [ "$pickans" = "n" -o "$pickans" = "N" ] ; then
echo ${editvar} > editvarfile.txt
kwrite editvarfile.txt
editvar=$(cat editvarfile.txt)
fi
done
rm editvarfile.txt

 

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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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