Ubuntu – Why are numeric function names not allowed

Several problems, in logical order of fixing:

• Style (pet peeve)

• With your ${...} statement in update_array(), the ${..} syntax to use a variable, not define it.

  Example:

  foo[0]=abc  # assigns 'abc' to foo[0]
  

• Working around that the array name is stored in a variable.

  Not working:

  $1[0]=abc
  

  Working:

  declare -g "$1[0]=abc"  # -g arg is for a global variable
  

• Passing an argument to update_array() should pass the variable name (foo in this case), not the contents of the array. foo[@] is nothing special, it is a completely normal string (in Bash).

• Variable expansion with ${foo[@]} should be double-quoted.

Working version of the code is below:

update_array() {   
    declare -g "$1[0]=abc"
}

foo=(foo bar)

update_array foo

for i in "${foo[@]}"; do
    echo "$i"
done

## Following line added by me for further clarification
declare -p foo

which prints, correctly:

abc
bar
declare -a foo='([0]="abc" [1]="bar")'

Based on testing:

• \0 is treated as marking the end of the password.
• Spaces are allowed. Though it isn't shown in the output below, by using CtrlV, I was able to use Enter, Esc and other keys in a password.

$ pwgen 10 1
Pohhei8sai 
$ passwd 
Changing password for muru.
(current) UNIX password: 
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
$ printf 'Pohhei8sai\n\0\b\n\0\b' | passwd
Changing password for muru.
(current) UNIX password: Enter new UNIX password: Retype new UNIX password: No password supplied
Enter new UNIX password: Retype new UNIX password: passwd: Authentication token manipulation error
passwd: password unchanged
$ pwgen 10 1
Uuxohv9moo 
$ printf 'Pohhei8sai\nUuxohv\09moo\nUuxohv\09moo\n' | passwd
Changing password for muru.
(current) UNIX password: Enter new UNIX password: Retype new UNIX password: Bad: new password is too simple
Enter new UNIX password: Retype new UNIX password: passwd: Authentication token manipulation error
passwd: password unchanged
$ printf 'Pohhei8sai\nUuxohv9moo\nUuxohv9moo\n' | passwd
Changing password for muru.
(current) UNIX password: Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully
$ printf 'Uuxohv9moo\ntesting 1\ntesting 1' | passwd
Changing password for muru.
(current) UNIX password: Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully

From my reading of the source, the passwd command uses the (obsolete) getpass function, which behaves pretty much like read -s (and marks the end of the password string with \0). It does not restrict the characters usable, aside from some checking of reuse and complexity. \0 cannot be used, since it gets treated as the normal end-of-string marker in C strings, but pretty much anything else can, such as the bell:

$ printf 'testing 1\nUuxohv\a9moo\nUuxohv\a9moo\n' | passwd
Changing password for muru.
(current) UNIX password: Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully