Reputation: 7915
I'm trying to execute a Fortran program in a shell from Python.
I'm using subprocess
to call the Fortran program and pass arguments (two input files are required). This is how I do it:
COMMAND = '/path/to/FORTRAN/program << !\n' + INPUT_FILE1 + '\n' + INPUT_FILE2 +'\n!'
return = subprocess.call(COMMAND, shell=True)
Unfortunately, the Fortran program exits with:
? FORTRAN Runtime Error:
? Attempt to read past end of file
? READ(UNIT=22,...
This is not an issue with the input files or the Fortran program. When I execute this in my shell:
$>/path/to/FORTRAN/program << !
>INPUT_FILE1
>INPUT_FILE2
>!
everything works as expected (no Attempt to read past end of file
).
I don't have access to the Fortran source, so I cannot check what is going on in there. I think it has to do with the way I'm calling the program through subprocess
- I just can't figure out what.
I'm using Python 2.6.6.
Quick explanation: The Fortran program will prompt for two input files, but it doesn't recognize them as command-line options (they cannot be provided with the call to the program). If you want to run it from - say a shell script (batch mode) - you need to capture the return command to execute the command, but also provide the two files. The << !
opens a "list" for lack of a better term. The following commands are handed to the program which waits with its execution until !
is typed.
I have used this approach multiple times successfully (different Fortran code), and with this one, using a C shell script (not Python).
Upvotes: 3
Views: 2012
Reputation: 414795
You could try "\r\n"
(tty newline):
from subprocess import Popen, PIPE
p = Popen(["/path/to/FORTRAN/program"], stdin=PIPE,
bufsize=1, close_fds=True)
p.communicate("INPUT_FILE1\r\nINPUT_FILE2")
rc = p.returncode
with/without "\r\n"
at the end.
Upvotes: 1
Reputation: 12990
Maybe it's caused by the shell invoked with shell=True
, if that doesn't invoke bash
on your system. You can avoid depending on the extended shell syntax <<
, and instead build the whole call on your own, as in:
popen = subprocess.Popen(["/path/to/FORTRAN/program"], stdin=subprocess.PIPE)
popen.stdin.write('123\n')
time.sleep(0.1) # hack, following LAK's suggestion
popen.stdin.write('456\n')
popen.stdin.close()
result = popen.wait()
Upvotes: 1