CentOS - Jun 2013 - [OT] bash here documents

Suppose I have this C++ program:
#include <iostream>
int main (int argc, char** argv)
{
    while (1)
    {
        char cmd[80];
        std::cin.getline(cmd, 80);
        std::cout << "response to " << cmd <<
std::endl;
    }
}

compiled by: c++ -o junk junk.cpp

and I have this bash script:
#!/bin/bash
./junk <<EOF
blah
bleh
\cC
EOF
echo "Something else"

When I run the script, the program starts and waits for input forever.
I have 2 questions:
1) The "blah" and "bleh" line are not echoed to cout. Why
not? Does the here document not send the data to stdin?
2) How do I terminate the program? When run interactively, I use <ctrl>-C.

Thanks,
Steve

In article <20130624135817.10QZO.129278.root at cdptpa-web19-z02>,
Steve <zephod at cfl.rr.com> wrote:
> Suppose I have this C++ program:
> #include <iostream>
> int main (int argc, char** argv)
> {
>     while (1)
>     {
>         char cmd[80];
>         std::cin.getline(cmd, 80);
>         std::cout << "response to " << cmd <<
std::endl;
>     }
> }
> 
> compiled by: c++ -o junk junk.cpp
> 
> and I have this bash script:
> #!/bin/bash
> ./junk <<EOF
> blah
> bleh
> \cC
> EOF
> echo "Something else"
> 
> When I run the script, the program starts and waits for input forever.
> I have 2 questions:
> 1) The "blah" and "bleh" line are not echoed to cout.
Why not? Does the here document not send the data to stdin?
> 2) How do I terminate the program? When run interactively, I use
<ctrl>-C.
You should be testing the return value from std::cin.getline() for
end-of-file. You are not testing it for any error. Always test return values.

In your script, the end of the here document will cause your program to see
end-of-file (this is NOT the string "EOF" - that's just the way
you denote
the end of the here doc).

And you really ought to find a forum or mailing list where this kind of
question is ON-topic. Flagging the subject OT isn't a magic permission
to post anything you like!

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

Steve wrote:
> Suppose I have this C++ program:
> #include <iostream>
> int main (int argc, char** argv)
> {
>     while (1)
>     {
>         char cmd[80];
>         std::cin.getline(cmd, 80);
>         std::cout << "response to " << cmd <<
std::endl;
>     }
> }
>
> compiled by: c++ -o junk junk.cpp
>
> and I have this bash script:
> #!/bin/bash
> ./junk <<EOF
> blah
> bleh
> \cC
> EOF
> echo "Something else"
>
> When I run the script, the program starts and waits for input forever.
> I have 2 questions:
> 1) The "blah" and "bleh" line are not echoed to cout.
Why not? Does the
> here document not send the data to stdin?
> 2) How do I terminate the program? When run interactively, I use
<ctrl>-C.
I've only done a tiny bit of C++, but a bunch of years of C. First, I
think the \cC is doing something odd; in vi, I'd have tried typing it in
with <ctrl-v><ctrl-c>. Second, do you want the output to be
"blah bleh"?

Finally, I am *very* strongly *not* a fan of while. If I have to use it, I
set *some* limit - in this case, I'd look for an end-of-file, or some word
you decide for "stop here".

As the old joke goes, about hunting elephants in Africa, a programmer sets
up a search patter up, across, up, back, starting in Capetown and ending
in Cairo.

The *experienced* programmer puts an elephant in the zoo in Cairo to
ensure termination of the loop.

          mark