[Discuss] Most reliable method to test if x server is running in a Bourne Shell script

[gaf at blu.org (Jerry Feldman)]

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Testing for the DISPLAY environment variable is unreliable because some
clients, such as Putty with X forwarding will set up DISPLAY even though
no x server is running. One way is to run an X application and test the
return code, but you would want that X app to return either success or
failure, but otherwise do nothing. IBM mainframes have a program,
IEFBR14 that simply returns (It is 1 line of code to branch to register 14).
Basically, what I want to do is something like:
#!/bin/sh
# The next line will execute in sh but not in tcl \
testxworking
# \
if [ $? = 0 ];then
# The backslash makes the next line a comment in Tcl \
exec wish "$0" ${1+"$@"}
# \
else
# \
 -- call a command line script
# \
exit
# \
fi
- ---

Basically, what I want to do is to bring up a GUI if X is available, or
simply run from the command line if not. BASH will execute the lines
that do not begin with a #, tcl (and wish) will not execute lines
preceeded by a '# \'.
But, the real issue is the line: testxworking. I want a short program
that returns 0 if an x server is present, and non-zero if not.



- -- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
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