1) #!/bin/bash -p
What is -p means ?

2) killall dhcpcd > dev/null 2 > & 1
What is 2 > & 1 means ?

3) if [ $? -ne 0 ]
then
ifconfig eth0 up;
exit 1;
fi
What is "$?" ? Does it refer to the last variable reference ?

4) suid putdata update &&
What is && means ?

I did look at the web site that gives instruction on BASH programming, but some of the things mentioned above was not covered.

1.) dunno. try man bash

2.)
2 refers to 'stderr'
> is redirection
1 is 'stdin'
& (in this context) is like addressof or whereabouts.
so this says: redirect stderr to where ever the hell stdin is headed. In this case both stdin and stderr are going to /dev/null so you'll never see any output

3.) I forget. again, man bash

4.) && is logical 'and'. I don't see what it'll do here, but it's like ./configure && make (configure and make, but don't make if configure fails).

all of these are answered in man bash. please check it out.

1) As far as I can make out from "man bash", -p stops bash reading a users startup files
2) 2>&1 means ouput the error stream to the standard output (the standard output is then ouptu to the file as has been specified)
3) $? contains the exit status of the last command
4) && means that the command will wait to be completed before continuing.

Just to be pendantic. . . && means will wait for SUCCESSFULL completion before continuing (i.e. exit status of 0). ;; means will wait for completion before continuing (any exit status).