11.9. setuid Scripts
Whoever runs a setuid program temporarily (as long as he or she is running the setuid program) becomes the owner of that program and has the same permissions as the owner. The passwd program is a good example of a setuid program. When you change your password, you temporarily become root, but only during the execution of the passwd program. That is why you are able to change your password in the /etc/passwd (or /etc/shadow) file, which is off-limits to regular users.
Shell programs can be written as setuid programs. You might want to do this if you have a script that is accessing a file containing information that should not be accessible to regular users, such as salary or personal information. If the script is a setuid ...
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