gdb - assign pipe output to a variable - gdb

Question

I have the following command , I would like to assign his output to a variable:
(gdb) pipe monitor get info | grep cross2_Release.nss | cut -c 3-13
0x566f80400
Tried this
set $main = 'pipe monitor get info | grep cross2_Release.nss | cut -c 3-14'
No symbol table is loaded. Use the "file" command.
Expected result would be to have $main equals to 0x566f80400

Answer 1

At first, I thought this would work:
python output = gdb.execute('pipe monitor get info | grep cross2_Release.nss | cut -c 3-13', to_string=True)
python gdb.set_convenience_variable('main', gdb.parse_and_eval(output))
But this fails because the pipe command sends output to GDB's stdout rather than to a stream that gdb.execute can capture and put into a string. So here's something a little more crude:
shell printf 'set $main = ' > ~/.gdbtmp
pipe monitor get info | grep cross2_Release.nss | cut -c 3-13 >> ~/.gdbtmp
source ~/.gdbtmp

Answer 2

Using the python subprocess.check_output() function it's relatively simple to do that:
py gdb.set_convenience_variable('main', gdb.parse_and_eval(subprocess.check_output('grep cross2_Release.nss | cut -c 3-13', shell=True, input=gdb.execute('monitor get info', to_string=True), text=True)))
But that's a lot to type, so I would pack that into a gdb convenience function:
import subprocess
class Pipe(gdb.Function):
def __init__(self):
super(Pipe, self).__init__("pipe")
def invoke(self, gdb_cmd, pipe_cmd):
return gdb.parse_and_eval(subprocess.check_output(pipe_cmd.string(), shell=True, input=gdb.execute(gdb_cmd.string(), to_string=True), text=True))
Pipe()
Which then could be used like this:
set $main = $pipe("monitor get info", "grep cross2_Release.nss | cut -c 3-14")