Re: read command not reading from pipe. why?

[Lorenzo Beretta <lory.fulgi@infinito.it>]

Foss User ha scritto:
> I see that the read command stores input entered only on the console
> into the variables. Example:
>
> $ read a
> foo
> $ echo $a
> foo
>
> But when I don't enter input on the console by keyboard, but pipe it
> into the standard input of read, I am unable to store the input into
> the variable.
>
> $ echo bar | read a
> $ echo $a
> foo
>
> However, the help of read says this:
>
> $ help read
> read: read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-p
> prompt] [-t timeout] [-u fd] [name ...]
>     Read a line from the standard input and split it into fields.
>
> So, why is it not reading the line from standard input when input is
> passed to it using a pipe?
Because the "read" is done in a child process, that starts, executes its 
instructions (ie: read), modifies its own private environment, and then 
dies, leaving the parent's environment untouched.
Try:

$echo qwerty | while read a ; do echo "a=$a" ; done
a=qwerty
$echo "a=$a"
a=


Hope that helped