Re: [Help-bash] confused by command substitution...

[Chet Ramey]

On 2/9/19 1:12 PM, Andy Chu wrote:
> This doesn't have to do with command subs, or even if statements.  The way
> I think of it is that a command line can evaluate to an empty argv array
> after splitting ("elision"), and then that empty argv array silently
> *succeeds*.

Or, as POSIX puts it when describing the results of word expansion on
simple commands:

"If there is no command name, but the command contained a command
substitution, the command shall complete with the exit status of the last
command substitution performed. Otherwise, the command shall complete with
a zero exit status."

So the command list following the if statement in both

if $(echo x >/dev/null); then echo ok; fi

and

if $(exit 42); then echo ok; fi

is a simple command, and both result in empty word lists after expansion,
but only the first one has a zero exit status.

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/