Hi Robin,
The eval command isn't evil, it is just dangerous to use it to evaluate any user supplied text. In a script, it can be used safely to evaluate commands when the command is entirely under the control of the script writer. For example to get the value of the last two command line arguments passed to a shell script, save the following in a file named last2:

Code:

#!/bin/ksh 
echo "${0##*/} has been called with $# arguments."
if [ $# -gt 1 ]
then    eval lm1=\$$(($# - 1))
else    lm1="There is only one argument."
fi
eval last=\$$# 
printf "The last two arguments are \"%s\" and \"%s\"\n" "$lm1" "$last"

and make it executable:

Code:

chmod +x last2

Then the command:

Code:

./last2 * '$(echo rm -rf ~loginID)'

will print:

Code:

last2 has been called with 9 arguments.
The last two arguments are "zebra" and "$(echo rm -rf ~loginID)"

if there are 7 files in the current directory and the last one (sorted alphabetically) is named zebra.

As Corona688 has already shown, if the script were then to use eval on the user supplied input stored in $last, the results could ruin the day for the user with the login name loginID!

Hi Corona688,
There are name reference variables in ksh93, but the syntax is different. In ksh you have to explictly state that a variable is to be treated as a reference variable using either the nameref or the typeset -n command. They can be used as shown here:

Code:

#!/bin/ksh
set -xv
x=123
nameref y=x
echo $y
echo ${!y}
y=456
echo $x
typeset -n z=x
echo $z
z="hello world"
echo $x

which produces the following combined stdout and stderr output:

Code:

x=123
+ x=123
nameref y=x
+ y=x
+ typeset -n y
echo $y
+ echo 123
123
echo ${!y}
+ echo x
x
y=456
+ x=456
echo $x
+ echo 456
456
typeset -n z=x
+ z=x
+ typeset -n z
echo $z
+ echo 456
456
z="hello world"
+ x='hello world'
echo $x
+ echo hello world
hello world