Re: [Help-bash] How to let a command take multiple here-doc?

[Peng Yu]

How to understand why the following code only print b?

cat <<EOF1 <<EOF2
a
EOF1
b
EOF2

It is not clear what the correct output should be based on POSIX.

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04

Also, the above link shows the following example. I am not sure why it
is usefully to intertwine the heredocs of the two separate commands.
Does anybody know?

cat <<eof1; cat <<eof2
Hi,
eof1
Helene.
eof2

On Fri, May 29, 2015 at 7:29 AM, Eric Blake <address@hidden> wrote:
> On 05/28/2015 09:34 PM, Dave Rutherford wrote:
>> On Thu, May 28, 2015 at 11:23 PM, Peng Yu <address@hidden> wrote:
>>> The following bash code uses cat twice. Because one uses EOF the other
>>> uses 'EOF', they can not readily be combined.
>>>
>>> x='Hello World!'
>>> cat <<EOF
>>> $x
>>> EOF
>>> cat <<'EOF'
>>> $x
>>> EOF
>>
>> This works as expected. What behavior are you looking for?
>>
>>> I can't find that that bash support multiple here-docs for the same
>>> command. Is it so?
>>
>> You mean one cat with two here-documents? You can't do that,
>> there's only one stdin.
>
> On systems with /dev/fd, you can do:
>
> $ cat - /dev/fd/4 <<EOF 4<<EOF
>> a
>> EOF
>> b
>> EOF
> a
> b
>
> for a single cat process that reads from two different fds.  But it's
> such an unusual idiom that I don't recommend it for code trying to be
> portable.
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>



-- 
Regards,
Peng