Re: [Help-bash] How to understand the blank space here

[Davide Brini]

On Mon, 26 Dec 2011 23:02:53 +0800, lina <address@hidden> wrote:

> Hi,
> 
> $ echo \"{Those, words, are, quoted}\"
> "{Those, words, are, quoted}"
> 
> I have a space after ,

Here bash sees four tokens after echo:

"{Those,

words,

are,

quoted}"

The double quote is part of the first and last argument, because you escaped
it with backslash. Those four tokens become arguments to echo, which
outputs them with a space in between them. Just as if you did

echo a b c d

you'd get

a b c d

as output.

> 
> echo \"{Those,words,are,quoted}\"
> "Those" "words" "are" "quoted"
> 
> Just wonder why the space there changed things,

Here you're seeing a different thing. This is brace expansion. First of
all, since there are no spaces, you're now creating a single token:

"{Those,words,are,quoted}"

The way brace expansion works is that each comma-separated word is
expanded to a separate argument; however, the brace expansion includes a
preamble (a double quote) and a postscript (again a single quote), so the
preamble and the postscript are prepended/appended to each of the generated
arguments, which is what echo finally sees. You can probably see it better
if you do this:

$ echo preamble_{a,b,c,d}_postscript
preamble_a_postscript preamble_b_postscript preamble_c_postscript 
preamble_d_postscript

The only difference is that in your case both the preamble and the
postscript are " (double quote).

-- 
D.