grep - How to find non-printable characters in the file?

I tried to find out the unprintable characters in data filein unix.
Code :

#!/bin/ksh

export SRCFILE='/data/temp1.dat'
while read line 
do
len=lenght($line)
for( $i = 0; $i < $len; $i++ ) {

        if( ord(substr($line, $i, 1)) > 127 )
        {
            print "$line\n";
            last;

        }
done < $SRCFILE

The code is not working , please help me in getting a solution for the above query.