Executing mail command from inside a function causes a "fork bomb"

Question

When I try to execute mail from inside a function in a bash script it creates something similar to a fork bomb. To clarify, this creates the issue:

#!/bin/bash

mail() {
    echo "Free of oxens" | mail -s "Do you want to play chicken with the void?" "example@example.org"
}

mail

exit 0

Sometimes you can just kill the command and it'll kill the child processes, but sometimes you'll have to killall -9.

It doesn't care whether the mail were sent or not. The fork bomb is created either way. And it doesn't seem as adding any check for the exit code, such as if ! [ "$?" = 0 ], helps.

But the script below works as intended, either it outputs an error or it sends the mail.

#!/bin/bash

echo "Free of oxens" | mail -s "Do you want to play chicken with the void?" "example@example.org"

exit 0

---

Why does this happen? And how would you go about checking the exit code of the mail command?

Answer 1

You're invoking the function mail from within the same function:

#!/bin/bash

mail() {
    # This actually calls the "mail" function
    # and not the "mail" executable
    echo "Free of oxens" | mail -s "Do you want to play chicken with the void?" "example@example.org"
}


mail

exit 0

This should work:

#!/bin/bash

mailfunc() {
    echo "Free of oxens" | mail -s "Do you want to play chicken with the void?" "example@example.org"
}

mailfunc

exit 0

Note that function name is no longer invoked from within the function itself.

Answer 2

Otherwise:

mail(){

    echo olly olly oxenfree | command mail -s 'and the rest' and@more
}

...should work fine.

Answer 3

The most "traditional" solution in these cases is actually to call the command with full path:

mail() {
    echo "Free of oxens" | /usr/bin/mail -s "Do you want to play chicken with the void?" "example@example.org"
}

All other answers work, and are probably more portable, but I think that this is the most likely solution you'd find in scripts in the wild real world, so I'm including it for completeness.