Help needed with perl crypt function

I am trying to generate a unique string/id given another relatively large string(consisting of a directory path name), thought of using crypt function. However, it's not working as expected, most probably due to my inability to understand.

here the code & output:

#!/usr/bin/perl 

print "Enter a string:"; 
chomp(my $string =开发者_Go百科 <STDIN>); 

my $encrypted_string = crypt($string,'di'); 

print "\n  the encrypted string is:$encrypted_string";

output:

$ perl crypt_test
 Enter a string:abcdefghi

 the encrypted string is:dipcn0ADeg0Jc
$
$ perl crypt_test
 Enter a string:abcdefgh

 the encrypted string is:dipcn0ADeg0Jc
$
$
$ perl crypt_test
 Enter a string:abcde

 the encrypted string is:diGyhSp4Yvj4M
$

I couldn't understand why it returned the same encrypted string for the first two strings and differed for the third one. Note that salt is same for all.

---

The crypt(3) function only takes into account the first eight chars of the input string:

By taking the lowest 7 bits of each of the first eight characters of the key, a 56-bit key is obtained. This 56-bit key is used to encrypt repeatedly a constant string (usually a string con‐ sisting of all zeros). The returned value points to the encrypted password, a series of 13 print‐ able ASCII characters (the first two characters represent the salt itself).

So what you are seeing is by design - from perlfunc:

crypt PLAINTEXT,SALT
       Creates a digest string exactly like the crypt(3) function in the C library