system("/cygdrive/c/CLISMS.exe /port=1 /ussd=*122#");
my $credit = qx(cat /cygdrive/c/Log.txt |grep \"Baki\" |tail -1 |cut -
+d, -f1);
$credit =~ s/Baki: //g;
$credit = floor($credit + 0.5);

if ($credit < 10) {
    system("/cygdrive/c/CLISMS.exe /port=1 /to=0133034931 /msg=[SMS Ga
+teway] URGENT!! Current prepaid credit is RM$credit.00, Please reload
+");
    #system("/cygdrive/c/CLISMS.exe /port=1 /to=0193301010 /msg=[SMS G
+ateway] URGENT!! Current prepaid credit is RM$cedit.00, Please reload
+");
}
[download]

/cygdrive/c/CLISMS.exe /port=1 /to=0133034931 /msg=[SMS Gateway] URGEN
+T!! Current prepaid credit is RM$credit.00, Please reload
[download]

should surely be

/cygdrive/c/CLISMS.exe /port=1 /to=0133034931 /msg='[SMS Gateway] URGE
+NT!! Current prepaid credit is RM$credit.00, Please reload'
[download]

What you have would have failed at the prompt too. Some of the characters you meant to pass as part of an argument apparently have a special meaning when you use them as part of a shell command.

I think command shell is trying to execute the value what you are passing to /cygdrive/c/CLISMS.exe. I think adding single quote around $val will help.

use Perl;
Perl4Everything