${!var} does not work in ksh

Shell Programming and Scripting
1

Anyone knows why the following function does not work in ksh (it does in bash)?

var() # Displays var value; case insensitive
{ 
  _var="$1"    

  if [ -n "${!_var}" ] ; then 
    echo ${!_var} 
  else 
    _var=$(echo "$_var" | tr 'a-z' 'A-Z') 
    echo ${!_var} 
  fi

  unset _var
}

$ var home
ksh: "${!_var}": 0403-011 The specified substitution is not valid for this command.

$ var path
/usr/local/bin:/usr/bin:/bin:/cygdrive/c/WINDOWS/system32:/cygdrive/c/WINDOWS:/cygdrive/c/WINDOWS/System32/Wbem:/cygdrive/c/Program Files/Support Tools:/cygdrive/c/Program Files/Hummingbird/Connectivity/7.11/Accessories/

Thanks!

Vic.

2

Not exactly sure, what ${!_var} does in Bash, but if you are just looking to get the value of a variable in ksh, you should use ${var}

3

I'm not trying to get the value of the variable, but use the value as a variable name.

Here's the difference:

BASH

$ _var=HOME
$ echo ${_var}
HOME
$ echo ${!_var}
/home/VMendonc

KORN

$ _var=HOME
$ echo ${_var}
HOME
$ echo ${!_var}
ksh: ${!_var}: 0403-011 The specified substitution is not valid for this command.
4

oh sorry... overlooked the reference to a variable there.

There is no direct way of accessing a variable using name reference in ksh. You need to use eval to do that:

> var="This is a variable"
> _var=var
> echo $_var
var
> eval echo \$$_var
This is a variable

If you use ksh93, however, there is a way to create name references:

> /bin/ksh93   ## Start a ksh93 shell
> var="This is a variable"
> typeset -n _var=var
> echo $_var
This is a variable

"typeset -n" creates a nameref to the given variable in ksh93, but this feature is not available in ksh (i.e., ksh88)

5

And if using a nameref in ksh93, ! is used to produce the actual reference:

$ nameref _var=HOME
$ echo $_var
/home/user
$ echo ${!_var}
HOME