var="abc"
expr substr $var 1 1
expr substr $var 2 1
expr substr $var 3 1

#!/usr/bin/env sh

# @(#) s1       Demonstrate sub-string extraction of parameter expansion.

set -o nounset
echo

## Define function to list versions.

version()
{
  for command
  do
    if command -v $command >/dev/null 2>&1
    then
      command -p $command --version | head -1
    else
      echo " (Warning -- command \"$command\" not found in PATH.)" >&2
    fi
  done
  return 0
}

## List the version of the commands in this demonstration.

version bash head

echo

s="xyz"
l=${#s}
echo " There are $l characters in |$s|"
echo

for ((i=0;i<l;i++))
do
        echo " Character $i of the string is |${s:$i:1}|"
done

exit 0

% ./s1

GNU bash, version 2.05b.0(1)-release (i386-pc-linux-gnu)
head (coreutils) 5.2.1

 There are 3 characters in |xyz|

 Character 0 of the string is |x|
 Character 1 of the string is |y|
 Character 2 of the string is |z|