Change directory in a shell script, and using expr

Question

I am just starting out with shell scripting (sh), and I have two issues.

Issue 1 : I'm trying to make a very simple script that creates a directory and immediately goes into it. This is the script I currently have:

#!/bin/sh
mkdir -p "$1"
cd "$1"

For some reason, this does not work. It creates the directory, but does not go into it. Am I missing something obvious here?

Issue 2 : I'm writing a very simple calculator that uses expr. But for the multiplication, I use x instead of * . So this is what I have right now:

#!/bin/sh

if test $# -lt 3
then
   echo "Usage calc [operand1] [operator] [operand2]"
   exit
fi

if test $2 = x
then
   op='\*'
else
   op=$2
fi

ret=`expr $1 $op $3`
echo $ret

This works for all the operations except multiplication. Calling calc 100 x 10 , for example, gives a syntax error. I tried different combinations, but I can't seem to get the right way of assigning \\* to op . What's the right way of doing it?

Answer 1

a) the script is run in a new shell. The cd doesn't apply to the outer. Try a shell alias instead of this script.

b) Quote parameters differently, in particular in expr