Strange bash sytax error depending on sudo usage

Question

I made this bash function to detect if the user running is actually logged in as root user and not using sudo by checking the uid + home directory of the user executing the command:

#!/bin/bash

set -x
function check_root(){
  home=`sh -c 'cd ~/ && pwd'`
  if [ "$home" != "/root" ] || [ "$(id -u)" != "0" ]; then
    echo -e "This script can only be executed by the root user, not with sudo  elevation"
  exit 1
  fi
}

check_root

When i run it as a regular user (uid 1000) it works as expected:

++ check_root
+++ sh -c 'cd ~/ && pwd'
++ home=/home/jake
++ '[' /home/jake '!=' /root ']'
++ echo -e 'This script can only be executed by the root user, not with sudo    elevation'
This script can only be executed by the root user, not with sudo elevation
++ exit 1

When i run it as root it also works as expected:

++ check_root
+++ sh -c 'cd ~/ && pwd'
++ home=/root
++ '[' /root '!=' /root ']'
+++ id -u
++ '[' 0 '!=' 0 ']'

But when i run it as regular user (uid 1000) with sudo elevation i get this:

./check_root.sh: 4: ./check_root.sh: Syntax error: "(" unexpected

System info:

Linux jake 3.11.0-26-generic #45~precise1-Ubuntu SMP Tue Jul 15 04:02:35 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

bash --version GNU bash, versie 4.2.25(1)-release (x86_64-pc-linux-gnu)

Answer 1

I had solved this in the mean time but did not yet post the solution - turned out to be syntax-related:

Working solutions:

function check_root {
 stuff..
}

and

function check_root () {
 stuff..
}

Eg removing the () from the function declaration or ensuring it is sepaerated by spaces at both sides fixes it.

Here's what i found in the bash manpage that made me spot the mistake :

Shell Function Definitions
       A shell function is an object that is called like a simple command and executes a compound command with a new set of positional parameters.  Shell functions are declared as follows:

       name () compound-command [redirection]
       function name [()] compound-command [redirection]
              This defines a function named name.  The reserved word function is optional.  If the function reserved word is supplied, the parentheses are optional

But.. i have no clue what exactly makes bash behave this way in this case.