On 12/17/09 6:02 AM, Zoltan Mate wrote:
> Dear Chet Ramey,
>
> I have a conversation on an other bug forum, then have been directed
> to here, I cannot find any documentation, why
You have to read the section on word splitting. The output of command
substitution is subject to word splitting, unless the substitution is
quoted.
> $ echo $(echo "'alfa beta'")
> gives 'alfa beta' whith reduced space, instead of the result of the
> following more logical ways:
>
> $ echo $(echo "'alfa beta'")
> the second term suggests one parameter being substituted as
> "<the output of the command>"
It helps to think about the output of each step in the word expansion
process and how that feeds the next step.
The command executed in a subshell is
echo "'alpha beta'"
The output is
'alpha beta'<newline>
which is read by the calling shell as the results of the command
substitution. The command substitution code removes the trailing newline
and passes the 'alpha beta' to the word splitting step.
Since that word is not quoted, it is subject to word splitting. The
splitting results in two words: "'alpha" and "beta'". Those two words
are passed to echo as separate arguments. echo outputs its arguments
separated by spaces and ends with a newline.
There is a program in the bash distribution named `recho' that makes it
clearer. When I run
recho $(echo "'alpha beta'")
I get the following:
argv[1] = <'alpha>
argv[2] = <beta'>
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
