Why does the following work from the prompt but fail when stuck inside a bash script? The bash script produces one empty line leading me to believe the variable isn't being set:
echo "red sox" | read my_var
echo $my_var
UPDATE: Since I guess my example isn't working, what I'm really trying to do is take I/O and pipe it into a variable to so I can do things with it. How do I do this? I thought this should be taken care of by the read command, but maybe there's another way?
It doesn't work at the prompt. My guess is you already have my_var set in your CLI, and are just retrieving that at the prompt.
Try this:
$ my_var="nothing"; echo "red sox" | read my_var; echo $my_var
If you want the my_var variable to have a constant value, as in your question, why not just do:
my_var="red sox"
If you are asking this because you simplified from a more general problem such as:
someprog args | read my_var
you should be using command substitution:
my_var=$(someprog args)
You can store the output of a command in a variable using either backticks or $() syntax:
my_var=`cat /some/file.txt`
Now the content of /some/file.txt is stored in $my_var. Same thing, with different syntax:
my_var=$(cat /some/file.txt)
Are you trying to pass args on the command line?
If so, $0 will contain the script name, and $1..n will contain command line args.
$@ will contain all command line args, space-separated.
What are you trying to do? Please explain what you wan't to do first.
If you're trying to set a variable this is what you need:
my_var="red sox"
echo $my_var
If you need it globally you should set it in env:
export my_var
The reason read doesn't work in a pipe the way you have it is that it creates a subshell. Variables set in a subshell don't persist to their parents. See BashFAQ/024.