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Top Forums Shell Programming and Scripting don't know how to interpret this Post 302503452 by Corona688 on Thursday 10th of March 2011 03:20:12 PM
Old 03-10-2011
Quote:
Originally Posted by Straitsfan
I guess I just should have asked what the statement

$listpage

means -- does it mean to display the value of listpage, and if so, why didn't it use the echo command?
Think more literally. It's just a variable, and the shell does the same thing with variables for every statement whether they're at the beginning of the line or the end. For each statement, the shell
1) Splits apart on semicolons or pipes, and evaluates each part(turns variables into their contents, etc).
2) Executes each part.
Code:
CMD="echo"
$CMD asdf

will print 'asdf' because it
1) converts $CMD asdf into echo asdf
2) runs "echo asdf".

Now this:
Code:
CMD="ls | more"
$CMD

does this:
1) Converts $CMD into ls | more
2) Executes ls | more

See something wrong? Pipes were supposed to be handled in step 1 but weren't, because it was in a variable. Step 2 doesn't do anything to pipes, so just feeds it into ls raw. ls complains there's no such files "|" and "more".

Now this:

Code:
CMD="ls | more"
eval "$CMD"

1) Converts eval "$CMD" into eval "ls | more"
2) Executes eval "ls | more", shoving the string "ls | more" back into step 1.
1) Splits ls | more into two statements, ls and more
2) Executes ls, piping it into more.

eval's just a special keyword that bumps the shell back into step 1.

Last edited by Corona688; 03-10-2011 at 04:25 PM..
 

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

NAME
sysprofile - modular centralized shell configuration DESCRIPTION
sysprofile is a generic approach to configure shell settings in a modular and centralized way mostly aimed at avoiding work for lazy sysad- mins. It has only been tested to work with the bash shell. It basically consists of the small /etc/sysprofile shell script which invokes other small shell scripts having a .bash suffix which are contained in the /etc/sysprofile.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 /etc/sysprofile. This mechanism is set up by inserting a small shell routine into /etc/profile for login shells and optionally into /etc/bashrc and/or /etc/bash.bashrc for non-login shells from where the actual /etc/sysprofile script is invoked: if [ -f /etc/sysprofile ]; then . /etc/sysprofile fi For using "sysprofile" under X11, one can source it in a similar way from /etc/X11/Xsession or your X display manager's Xsession file to provide the same shell environment as under the console in X11. See the example files in /usr/share/doc/sysprofile/ for illustration. For usage of terminal emulators with a non-login bash shell under X11, take care to enable sysprofile via /etc/bash.bashrc. If not set this way, your terminal emulators won't come up with the environment defined by the scripts in /etc/sysprofile.d/. Users not wanting /etc/sysprofile 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/.nosysprofile in the user's home directory using e.g. the touch(1) command. Any single configuration file in /etc/sysprofile.d/ can be overridden by any user by creating a private $HOME/.sysprofile.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/sysprofile.d/ configuration files. Empty versions of these files contained in the $HOME/.syspro- file.d/ directory automatically disable sourcing of the system wide version. Naturally, users can add and include their own private script inventions to be automagically executed by /etc/sysprofile at login 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 /etc/sysprofile.d/ and the manual pages 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 logout time check out the related package syslogout(8) which is a very close compan- ion to sysprofile. BUGS
sysprofile 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
sysprofile 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. SYSPROFILE(8)
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