How can I “try to do something and then detect if it fails” in bash?

Question

In an answer to a previous question:

How can I use 'do I have root access?' as a conditional in bash?

The suggestion to \'try to do something and de

Answer 1

if sudo chmod a-x /etc/shadow 2>/dev/null
then : Yes - I have root permissions
else : No - I do not have root permissions or /etc/shadow does not exist or ...
fi

This chooses an operation that does no damage if it succeeds (the shadow password file is not supposed to be executable; you could do something like chmod o-w / - remove public write permission from the root directory if you prefer), and check that it worked by looking at the exit status of the command. This throws away the error message - you have to decide whether that matters.

The 'sudo' is there to raise the privileges; if you think the user should already be 'root', then omit the 'sudo'.