Advanced variable usage

Arrays

Yes, you CAN have arrays in ksh, unlike old bourne shell. The syntax is as follows:


# This is an OPTIONAL way to quickly null out prior values
set -A array
#
array[1]="one"
array[2]="two"
array[3]="three"
three=3

print ${array[1]}
print ${array[2]}
print ${array[3]}
print ${array[three]}

Special variables

There are some "special" variables that ksh itself gives values to. Here are the ones I find interesting

PWD - always the current directory
RANDOM - a different number every time you access it
$$ - the current process id (of the script, not the user's shell)
PPID - the "parent process"s ID. (BUT NOT ALWAYS, FOR FUNCTIONS)
$? - exit status of last command run by the script
PS1 - your "prompt". "PS1='$PWD:> '" is interesting.
$1 to $9 - arguments 1 to 9 passed to your script or function

Tweaks with variables

Both bourne shell and KSH have lots of strange little tweaks you can do with the ${} operator.
The ones I like are below.

To give a default value if and ONLY if a variable is not already set, use this construct:


APP_DIR=${APP_DIR:-/usr/local/bin}

(KSH only)
You can also get funky, by running an actual command to generate the value. For example


DATESTRING=${DATESTRING:-$(date)}

(KSH only)
To count the number of characters contained in a variable string, use ${#varname}.


  echo num of chars in stringvar is ${#stringvar}