To make sure your script is compatible with *pure* bourne shell – if you don’t actually have it (not available for Linux it seems) you might want to grab source code of Heirloom Bourne Shell, compile and install it – also comes with nice man page where you can easily check what is possible with it and then if not sure you can view if something you have used to in bash is possible – the man page is much shorter and easier to read than bash man page as the features are SO much more limited

For those wanting to make sure their script is Bourne Shell compatible but you don’t have actual Bourne Shell available, Heirloom Bourne Shell is something you may want to look into – comes in source package, no configure script, you just have to edit very simple modifications to very simple Makefile, compile and install and you have Bourne Shell with NO extensions whatsoever – with that I’ve learned a lot on how much imagination and crazy hacks you may have to achieve to do things that in Bash are quite normal things to do It may be fun, I for one like to do some hobby projects “just to see if I can” where I try to do something in Bourne Shell – like transforming script relying on recursive function calls into Bourne Shell which has no function local variables, only script global ones (hint: subprocess inside function can help, of course the things you can do are limited, subprocess can have it’s own variables, but you can’t change variables outside it, he-he).

Great post.

Shell scripts – being readable as well as executable, and particularly being in plain-text also – are especially vulnerable to attack, as an attacker can see how their input will be treated before even attempting to exploit the script. Anything they get the script to run, will be run with superuser privileges.

1 mkdir -p
2 ?
3 ?
4 Use doble quotes only when it´s really needed?
5 Mmmmh I understand use \n instead the enter itself, but why? what’s the difference?
6 Group… in a file and execute? or maybe use pipes?
7 Why use xargs instead find -exec
8 Detect when is usefull grep and when “grep -c”
9 awk ‘$2~/RegExp/’ instead grep “RegExp”
10 That’s classic stop using cat to pipe the output to another command

PS. There’s no need for ‘-p “”‘, it should default to a blank prompt

n=0 # n being the number of (valid) data provided
sum=0 # sum being the running total of all data

# “Note that by using ^D (aka “EOF”) to quit, this script will work just as well blah blah”
# — Thanks, so i can make a function out of this and pipe data directly into it =)

function calc_avg() {
while read -p “” x; do
sum=`expr $sum + $x` && n=$[n+1] # “expr” return status indicates if valid integer or not
done

# ok, finished adding, now calculate the average.
echo “scale=2;$sum/$n” | bc
}

# like said above, just pipe $* args through calc_avg with a newline between each one.
echo $* | tr ‘ ‘ ‘\n’ | calc_avg

### TODO: write a version that accepts floating point numbers as arguments ###