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Full Discussion: Check if variable is set in script
Top Forums Shell Programming and Scripting Check if variable is set in script Post 81187 by vino on Wednesday 17th of August 2005 05:37:26 AM
Old 08-17-2005
Use ksh. ksh has shell builtin's to check for those conditions.

From man ksh under the Parameter sub-heading.

Code:
       Modifiers can be applied to the ${name} form of parameter substitution:

       ${name:-word}
              if  name  is set and not null, it is substituted, otherwise word
              is substituted.

       ${name:+word}
              if name is set and not  null,  word  is  substituted,  otherwise
              nothing is substituted.

       ${name:=word}
              if  name is set and not null, it is substituted, otherwise it is
              assigned word and the resulting value of name is substituted.

       ${name:?word}
              if name is set and not null, it is substituted,  otherwise  word
              is  printed  on  standard error (preceded by name:) and an error
              occurs (normally causing termination of a shell script, function
              or  .-script).  If word is omitted the string ?parameter null or
              not set? is used instead.

       In the above modifiers, the : can be omitted, in which case the  condi-
       tions  only  depend on name being set (as opposed to set and not null).
       If word is needed, parameter, command, arithmetic and  tilde  substitu-
       tion are performed on it; if word is not needed, it is not evaluated.

Have a look at examples given in the orielly book Learning the Korn Shell

Vino
 

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LEARN ABOUT BSD

shift

shift(1)							   User Commands							  shift(1)

NAME

       shift - shell built-in function to traverse either a shell's argument list or a list of field-separated words

SYNOPSIS

   sh
       shift [n]

   csh
       shift [variable]

   ksh
       * shift [n]

DESCRIPTION

   sh
       The positional parameters from $n+1 ... are renamed $1 ... . If n is not given, it is assumed to be 1.

   csh
       The  components of argv, or variable, if supplied, are shifted to the left, discarding the first component. It is an error for the variable
       not to be set or to have a null value.

   ksh
       The positional parameters from $n+1 $n+1 ... are renamed $1 ..., default n is 1. The parameter n can  be  any  arithmetic  expression  that
       evaluates to a non-negative number less than or equal to $#.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words,  following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
	   able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation  are  not
	   performed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), ksh(1), sh(1), attributes(5)

SunOS 5.10							    15 Apr 1994 							  shift(1)
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