Bash: all variables are arrays. Why?

catkin · 09-09-2009, 08:41 AM

Hello

Is the following behaviour documented anywhere?

Code:

c@CW8:~$ scalar='string'
c@CW8:~$ echo ${#scalar[*]}
1
c@CW8:~$ echo ${scalar[0]}
string

Best

Charles

RaptorX · 09-09-2009, 08:46 AM

Quote:

Is the following behaviour documented anywhere?

Yes... Everywhere...

Actually what happens is that bash variables are untyped.

That means that it will treat that variable as you are referring to it at the moment.

this link should clarify that for you.

this little quote is also an example of it:

Quote:

Bash permits array operations on variables, even if the variables are not explicitly declared as arrays.

string=abcABC123ABCabc
echo ${string[@]} # abcABC123ABCabc
echo ${string[*]} # abcABC123ABCabc
echo ${string[0]} # abcABC123ABCabc
echo ${string[1]} # No output!
# Why?
echo ${#string[@]} # 1
# One element in the array.
# The string itself.

# Thank you, Michael Zick, for pointing this out.

Once again this demonstrates that Bash variables are untyped.

catkin · 09-09-2009, 09:04 AM

Thanks RaptorX

I knew bash variables are untyped -- but not that it went as far as scalar variables being single element arrays! Truly bash is full of surprises!

Best

Charles

RaptorX · 09-09-2009, 09:17 AM

I didnt see it was you!

Im talking like a teacher to my teacher.

catkin · 09-09-2009, 09:37 AM

That's the great thing about co-operation, huh?

The day we stop learning is, er, ... the day we don't learn any more!

The ABSG is a great resource, especially for examples, but I always turn to the GNU Bash Reference Manual and the The Open Group's Shell Command Language Specialisation when in doubt. I couldn't find anything relevant in them so posted ... and you gave me the answer, thank you.

RaptorX · 09-09-2009, 09:52 AM

You know that I have been reading this Advanced Bash Scripting thingy... it is actually a wealth of information and I dont find it sleep provoking as the bash manual (I cant read more than 2 pages of man bash)

It is something that almost all linux users should read even if is a quick read.

[edit]

Actually my answer to your other post (the one with $[]) comes also from the ABS book.