saving contents of echo output to variable in non-bash script

Question

I'm used to doing something like this in my bash scripts to echo output to a variable:

myvar=`echo $OSTYPE`
echo "my os is of type: ${myvar}"

On this current project however I'm using sh, which on my Ubuntu instance doesn't appear to be symlinked to bash. I say that because the above code echoes nothing for ${myvar} when I have the /bin/sh shebang at top.

So I assume echo $OSTYPE is not the way to go in sh? If not, how can I do something similar? (I've tried to echo $(myvar) but that didn't work either.)

Answer 1

The following seems to work just fine in my sh :

$ myvar="test"
$ echo "My var is $myvar."
My var is test.

There is no need to echo the value of the variable and catch it again in another. Here is a little bit more information on variable assignments.

The thing is, OSTYPE is not defined in sh's environment. You'll have to pass it when running your script. So, instead of running...

$ /bin/sh yourscript.sh
or
$ ./yourscript.sh

You should run:

$ OSTYPE=$OSTYPE /bin/sh yourscript.sh
or
$ OSTYPE=$OSTYPE ./yourscript.sh

Of course, this assumes that the parent shell, in which you type the above command, has an OSTYPE variable. While bash does, it is not the case of every shell. Instead of $OSTYPE, you might however be able to use uname:

$ OS=$(uname -o)
$ echo "My OS is $OS."
My OS is GNU/Linux.
$ echo "My OS is $(uname -o)."
My OS is GNU/Linux.

On my machine, this sets the OS variable to GNU/Linux, instead of linux-gnu (which is the content of my OSTYPE).

As a side note, I'm guessing an equivalent of your code could be :

$ myvar="$(echo $OSTYPE)"
$ echo "My var is $myvar."
My var is linux-gnu