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Full Discussion: quick question
Top Forums Shell Programming and Scripting quick question Post 66931 by S.Vishwanath on Friday 18th of March 2005 05:15:35 AM
Old 03-18-2005
Ya, as explained by Bhargav, it gives the return value of the Previous command.
In the above, when you run the jfdfkjd at the prompt, which is not a valid command, the system (shell) fired with command not found...and so when you immediately check $?, it give the return (exit status) of the previous command, and since the value is greater than 0, says that the previous command was an abnormal kind of operation.
Where as next time when data was executed, since its a valid command, it did work fine and hence when you immediately execute $? it return 0 saying that the previuos unix operation was a normal/smooth/perfect operation.

Even you can follow the similar decipline in your programming either C or Shell scripting (use exit 0 in shell script to indicate operationg was smooth else use exit <any greater than zero value> to indicate a failure operation.) This is a good dicipline programming approach.

Small Test, try this..at the command prompt prompt

abcd
echo $?
echo $?
ls
echo $?
echo $?
abcd
echo $?
echo $?
echo $?
-->All the best in your test.
 

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LEARN ABOUT DEBIAN

vtysh

VTYSH(1)							  Version 0.96.5							  VTYSH(1)

NAME

       vtysh - a integrated shell for Quagga routing software

SYNOPSIS

       vtysh [ -b ]
       vtysh [ -E ] [ -d daemon ] ] [ -c command ]

DESCRIPTION

       vtysh is a integrated shell for Quagga routing engine.

OPTIONS

       Options available for the vtysh command:

       -b, --boot
	      Execute  boot  startup configuration. It makes sense only if integrated config file is in use (not default in Quagga). See Info file
	      Quagga for more info.

       -c, --command command
	      Specify command to be executed under batch mode. It behaves like -c option in any other shell - command is executed and vtysh exits.

	      It's useful for gathering info from Quagga routing software or reconfiguring daemons from inside shell scripts, etc.  Note that mul-
	      tiple commands may be executed by using more than one -c option and/or embedding linefeed characters inside the command string.

       -d, --daemon daemon_name
	      Specify  which  daemon to connect to.  By default, vtysh attempts to connect to all Quagga daemons running on the system.  With this
	      flag, one can specify a single daemon to connect to instead.  For example, specifying '-d ospfd' will connect only to  ospfd.   This
	      can be particularly useful inside scripts with -c where the command is targeted for a single daemon.

       -e, --execute command
	      Alias  for  -c.  It's  here  only  for  compatibility with Zebra routing software and older Quagga versions. This will be removed in
	      future.

       -E, --echo
	      When the -c option is being used, this flag will cause the standard vtysh prompt and command to be echoed prior  to  displaying  the
	      results.	This is particularly useful to separate the results when executing multiple commands.

       -h, --help
	      Display a usage message on standard output and exit.

ENVIRONMENT VARIABLES

       VTYSH_PAGER
	      This should be the name of the pager to use. Default is more.

FILES

       /usr/local/etc/vtysh.conf
	      The default location of the vtysh config file.

       /usr/local/etc/Quagga.conf
	      The default location of the integrated Quagga routing engine config file if integrated config file is in use (not default).

WARNING

       This man page is intended to be a quick reference for command line options. The definitive document is the Info file Quagga.

SEE ALSO

       bgpd(8), ripd(8), ripngd(8), ospfd(8), ospf6d(8), isisd(8), zebra(8)

BUGS

       vtysh eats bugs for breakfast. If you have food for the maintainers try http://bugzilla.quagga.net

AUTHORS

       See http://www.zebra.org and http://www.quagga.net or the Info file for an accurate list of authors.

Quagga VTY shell						   27 July 2006 							  VTYSH(1)
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