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Top Forums Shell Programming and Scripting What does : do in this instance Post 302313999 by methyl on Thursday 7th of May 2009 07:35:52 AM
Old 05-07-2009
: is an alias for "true". See "man true" (though it is also built into ksh). It is a command which does nothing and returns exit status 0. The loop will keep going until it is exited.
In the second example the ":" is being used cleverly as a null command to allow the "${ans:=y}" default substitution to work without giving a syntax error.
 

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shell(1F)							   FMLI Commands							 shell(1F)

NAME
shell - run a command using shell SYNOPSIS
shell command [command] ... DESCRIPTION
The shell function concatenate its arguments, separating each by a space, and passes this string to the shell ($SHELL if set, otherwise /usr/bin/sh). EXAMPLES
Example 1: A sample output of shell command. Since the Form and Menu Language does not directly support background processing, the shell function can be used instead. `shell "build prog > /dev/null &"` If you want the user to continue to be able to interact with the application while the background job is running, the output of an exe- cutable run by shell in the background must be redirected: to a file if you want to save the output, or to /dev/null if you don't want to save it (or if there is no output), otherwise your application may appear to be hung until the background job finishes processing. shell can also be used to execute a command that has the same name as an FMLI built-in function. NOTES
The arguments to shell will be concatenate using spaces, which may or may not do what is expected. The variables set in local environments will not be expanded by the shell because "local" means "local to the current process." ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
sh(1), attributes(5) SunOS 5.10 5 Jul 1990 shell(1F)
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