How do I push a subprocess.call() output to terminal and file?

Question

I have subprocess.call(["ddrescue", in_file_path, out_file_path], stdout=drclog). I'd like this to display the ddrescue in the terminal as it's running and write the output to the file drclog. I've tried using subprocess.call(["ddrescue", in_file_path, out_file_path], stdout=drclog, shell=True), but that gives me an input error into ddrescue.

Answer 1

If ddrescue doesn't change its output if its stdout/stderr are redirected to a pipe then you could use tee utility, to display output on the terminal and to save it to a file:

$ ddrescue input_path output_path ddrescue_logfile |& tee logfile

If it does then you could try to provide a pseudo-tty using script utility:

$ script -c 'ddrescue input_path output_path ddrescue_logfile' -q logfile

If it writes directly to a terminal then you could use screen to capture the output:

$ screen -L -- ddrescue input_path output_path ddrescue_logfile

The output is saved in screenlog.0 file by default.

---

To emulate the tee-based command in Python without calling tee utility:

#!/usr/bin/env python3
import shlex
import sys
from subprocess import Popen, PIPE, STDOUT

command = 'ddrescue input_path output_path ddrescue_logfile'
with Popen(shlex.split(command), stdout=PIPE, stderr=STDOUT, bufsize=1) as p:
    with open('logfile', 'wb') as logfile:
        for line in p.stdout:
            logfile.write(line)
            sys.stdout.buffer.write(line)
            sys.stdout.buffer.flush()

To call the tee-based command in Python using shell=True:

#!/usr/bin/env python
from pipes import quote
from subprocess import call

files = input_path, output_path, ddrescue_logfile
rc = call('ddrescue {} |  tee -a drclog'.format(' '.join(map(quote, files))),
          shell=True)

To emulate the script-based command:

#!/usr/bin/env python3
import os
import shlex
import pty

logfile = open('logfile', 'wb')
def read(fd):
    data = os.read(fd, 1024) # doesn't block, it may return less
    logfile.write(data) # it can block but usually not for long
    return data
command = 'ddrescue input_path output_path ddrescue_logfile'
status = pty.spawn(shlex.split(command), read)
logfile.close()

To call screen command in Python:

#!/usr/bin/env python3
import os
import shlex
from subprocess import check_call

screen_cmd = 'screen -L -- ddrescue input_path output_path ddrescue_logfile'
check_call(shlex.split(screen_cmd))
os.replace('screenlog.0', 'logfile')