What is the difference between using an environment variable, like PATH, as $PATH or ${PATH}?
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3 Answers
There's no difference in most cases. The only times it matters is if you want to include trailing text after the expansion. For example, suppose your PATH contained the string FOO (not actually a valid path, but this is for an example), and you wanted to form the string FOOBAR. If you did
$PATHBAR
You would get the expansion of the variable named PATHBAR, which is probably not what you wanted. If you did
$PATH BAR
You would get a space between FOO and BAR, also not what you wanted. The solution is to use braces:
${PATH}BAR
This gives you FOOBAR.
answered Sep 12, 2009 at 20:22
Adam Rosenfield
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PATH is the name of the environment variable, $PATH and ${PATH} are methods of accessing them. The form ${PATH} is used to allow constructs like echo ${PATH}b which would fail using $PATHb. Also, bash allows lots of parameter replacement stuff which the man page will gladly tell you more about.
2 Comments
mk12
what does the
b after ${PATH} mean?
Nicholas Riley
It'll put a literal "b" after PATH instead of accessing an environment variable named PATHb. Try it yourself.
In your case there is no difference, but - take the situation: You have two variables:
$FOO = "YA"
$YADA = "bar"
then ${$FOODA} will give you nothing while ${${FOO}DA} will give you "bar"
2 Comments
Bryan Oakley
'$FOO = "YA"' is incorrect -- it doesn't do what you think it does. You need to do 'FOO-="YA"'
William Pursell
No, ${${FOO}DA} will give you a syntax error, but eval '$'{${FOO}DA} will give the contents of $YADA...if you assign to FOO correctly.