What does : do in this instance Post: 302313978

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Top Forums Shell Programming and Scripting What does : do in this instance Post 302313978 by lavascript on Thursday 7th of May 2009 06:42:05 AM

05-07-2009

Registered User

What does : do in this instance

Guys please see below functions to return a status depending on user input. Both seem to work the same.

The second way has a : line which i can't understand or see in a ksh manual anywhere. Instead of doing the variable change if its empty on this line the first function simply does it on the case line. They both work but which is best and what does the : do?

Code:

confirm_yes()
{
          messages="$1"
          while :
          do
              print "${messages} [yn,] (default y)"
              read ans
              case ${ans:=y}
                   N*|n*) return 1 ;;
                   Y*|y*) return 0 ;;
                   *) print "You have entered an invalid option. Try again"
              esac
          done
}

Second way

Code:

confirm_yes()
{
          Valid=1
          while [ $Valid = 1 ]
          do
              echo "${1} [yn,] (default y)"
              read ans
              :      ${ans:=y}
              case ${ans}
                   N*|n*) return 1 ;;
                   Y*|y*) return 0 ;;
                   *) echo "You have entered an invalid option. Try again"
              esac
          done
}

This is for ksh script and function is called by :-

Code:

if confirm_yes "Would you like to unfreeze me?" ;then
        blah blah blah.......
else
        woa woa woa.....
fi

Cheers

lavascript

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LEARN ABOUT X11R4

shell

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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