Decrypting may be impossible, but you don't have to decrypt it -- you just have to find something that creates the same string when encrypted using the same routines through brute force.

Computer security is a bit of a misnomer -- it's never secure in an absolute sense, it just has an acceptable risk, normally by using mechanisms that will attempt to reduce a person's chance of managing to gain access without permission before the information loses its value down to an acceptable level.

But now, we get to the real question -- why is the password in the file? All of these suggestions to store the password using a one way encryption are great, if the script is authenticating a user giving the password. If the script is a client, and needs the password to connect to another service, those suggestions aren't useful.

The original poster might be interested in the thread Quest: a bulletproof-secure, automated scraper, which had a few suggestions on better protecting a password, but they all just slow down someone trying to get the password, and they're not likely to have a whole lot of help on a system where you don't trust people with root access, who could just change the code to write the unencypted/unobfuscated password before it makes use of it.

What I took the OP to be asking was how to hide a password which they need to provide to something else (e.g. to a database or an Expect driven ssh session). In that case having a hashed password does you no good, which is why I didn't mention it (the original question was too vague to call it either way).