Sorry, there is something screwy with your system. Getting the exact same hash value for the exact same data is a design goal of any hash algorithm worth using.

This is what I get on your code:

$ cat test.pl
#!/usr/local/bin/perl
use Digest::SHA1;
# encrypts password using
# SHA-1 algorithm
my $sha1 = Digest::SHA1->new;

# reset algorithm
$sha1->hexdigest;

# encrypt
$passwd = 'password';
$salt = 1658087940;
my $secret = $sha1->sha1_hex($passwd . $salt);

print "Secret: ", $secret, "\n";

$ ./test.pl 
Secret: c757584a6cff45409cdf716903aa363e95354860

$ ./test.pl 
Secret: c757584a6cff45409cdf716903aa363e95354860
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