How to add a password to a specific command

To achive what you want I can propose the following:

1. Create a user for each program. In your example suppose you create a user uxxd (group uxxd).
2. Give it the password you want (form your example 123456)
3. Give the execution rights on this program only to user uxxd: chown uxxd:uxxd xxd chmod 700 xxd
4. For better security you could also remove the login shell from the user uxxd (depending on you system you can replace it with /bin/nologin for example)

Now to launch your program you need:

su uxxd -c xxd

If this program is supposed to create files for user who started it, the user probably should be in the group uxxd. This depends on the default umask on your system and can be changed.

Sorry for the late reply.

I used other command and not xxd since it cannot support a password.

I used openssl command in which I can put a password everytime I encrypt a password:

openssl enc -aes-128-cbc -a -salt -pass pass:test123

Now, if I need to decrypt it. I need to use:

openssl enc -aes-128-cbc -a -d -salt -pass pass:test123

Thanks for the help everyone.

This isn't so secure

you could add this to /etc/profile

xxd()
{
if [ $1 = "123456" ]; then
xxd ${@:2}
else
echo "sorry command not available"
fi
}

/usr/bin/xxd()
{
if [ $1 = "123456" ]; then
xxd ${@:2}
else
echo "sorry command not available"
fi
}

you'd run the command as xxd 123456 -r ...

you'd have to restrict read access to the binary though so it can't be copied.

any user could also read /etc/profile and see the password, you could possibly put these in a script xxdcmd.sh with no read access, and have it run somehow.

Anyhow i think a good solution would be what was suggested about having a user/group, but i thought it would be interesting to find other methods.

Cheers!

PS: this would be a good solution to what you're ultimately trying to achieve

gpg -c <filename>
gpg -d <filename.gpg>