Saturday, May 10, 2008

Finding the Number of Characters In A Variable Regardless Of Your Linux Or Unix Shell

Hey there,

Here's a simple enough task: Finding (or determining) the amount of characters in a string variable. In most Unix or Linux shells, this has become a trivial exercise. For instance, in bash or ksh, you can easily tell how many characters are in a particular string variable by either writing one line of code, or skipping right to the end and printing out the answer. By way of example:

host # x=thisIsMyVariable
host # echo ${#x}

And it's that simple. The variable x, which contains the string value "thisIsMyVariable", does, indeed, contain 16 elements (or characters). As you can see, in the more advanced shells, taking care of this is no problem.

However, in certain circumstances, you may be required to use a less-advanced, but more highly-portable, shell, like the original Bourne shell. In that case, this same sequence of commands would result in the following:

host # x=thisIsMyVariable
host # echo ${#x}
host #
<--- At best, you'll get zero here. Expect nothing. You might possibly get an error.

Our script attached today, uses the old-style expr (Well, it uses the new style expr with the old format and options, again, for maximum portability between systems and shells). It does the exact same thing that echo'ing ${#VARIABLE_NAME} does, but goes about it in a grueling and confusing manner. Remember back when you had to write scripts that took the shell's needs into consideration before your own? ;) Nowadays, things are much more intuitive.

Given a string, like "thisIsMyVariable," the following script will produce the exact same results. It will spit out how many characters are in that string, but take a longer, more confusing ,route to the answer. This is another good example of security through obfuscation as well. In general, having to use the expr command can be a hurdle for folks who've never used a shell that can't do arithmetic or string comparison on its own :)

Sample output (as boring as it is ;):

host # ./ thisIsMyVariable

And now, you can get the string length no matter how limited your shell is!


Creative Commons License

This work is licensed under a
Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License


# - print out how many characters are in a string variable
# 2008 - Mike Golvach -
# Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

if [ $# -ne 1 ]
echo "Usage: $0 string"
exit 1

echo $string|while read x
chars=`expr "$x" : '.*'`
echo $chars

, Mike