[ale] OT: Sending Commands to GDB

[Ed Cashin]

Sometimes it's easier to use "expect" than to figure out
what's going wrong.

On Wed, Jan 19, 2011 at 11:51 AM, Brian Pitts <brian at polibyte.com> wrote:
> On 01/19/2011 09:25 AM, Tim Watts wrote:
>> More progress. Try this:
>>
>> #!/bin/bash
>> sleep 0.5
>> cat
>> echo quit
>> sleep 0.5
>>
>> and this:
>>
>> $ echo pwd |./gdbin|gdb /bin/true
>
> This is interesting Tim, thanks for your help. You too Michael. You put
> me on the write track to play around with Python's subprocess module.
> The communicate() method
>
> 1. (optionally) sends data to stdin
> 2. reads data from stdout and stderr, until end-of-file is reached.
> 3. Waits for process to terminate.
>
> g = subprocess.Popen('gdb /bin/true', shell=True, stdin=subprocess.PIPE,
> stdout=subprocess.PIPE)
>
> g.communicate('pwd\n')
>
> Not surprisingly based on our experiences, the pwd command was not
> executed. The only output after the missing debuginfo warnings is
>
> (gdb) Hangup detected on fd 0\nerror detected on stdin\n
>
> But what if I write to stdin before calling communicate?
>
> g = subprocess.Popen('gdb /bin/true', shell=True, stdin=subprocess.PIPE,
> stdout=subprocess.PIPE)
>
> g.stdin.write('pwd\n')
>
> g.communicate()
>
> Like your experiments suggested, this works. The last of the output is
>
> (gdb) Working directory /home/brian.\n(gdb) Hangup detected on fd
> 0\nerror detected on stdin\n
>
> If I throw in a
>
> g.stdin.write('quit\n')
>
> I can avoid the final hangup and error messages.
>
>> [BTW, how is this OT?]
>
> I don't remember why I thought the post would be OT when I started
> writing it last night. It didn't end up that way.
>
> --
> All the best,
> Brian Pitts
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-- 
  Ed Cashin <ecashin at noserose.net>
  http://noserose.net/e/
  http://www.coraid.com/