I have a bunch of environment variables passed from client code, if they are not set, I need to set default values to them.
Except testing them one by one with a lot of if ...; then ... fi, is there a clean way to do this?
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2 Answers
You can use parameter expansion like this:
foo=${foo:-default value}
This will set $foo to "default value" if it is not defined or empty(!).
Note that using the above code, you can't distinguish between a variable which has not being defined and a variable which has been explicitly set to an empty string. If that's fine for you, use it.
You can have two files:
- a file containing the default value of variables.
- the client file
Source the default file and then the one from the client. This way, customer's values will be overwritten.
Test
Let's have these two files:
$ cat default
export var1="foo"
export var2="bar"
export var3="bee"
$ cat customer
export var2="yeah!"
Now, let's source them:
$ source default
$ env | grep "^var"
var1=foo
var3=bee
var2=bar
Then let's get customer's file:
$ source customer
$ env | grep "^var"
var1=foo
var3=bee
var2=yeah!
As you see, variable $var2 has not the value from customer's file, whereas the others have the value sest in default.
2 Comments
dotslashlu
Wow! Much cleaner and easier to maintain than the parameter expansion way, thanks.
fedorqui
@LotusH nice that it was useful for you : )