I have a job that produces output continually. I want to write this output to a Vim buffer. I start it with:

let job = job_start(cmd, { 'out_io': 'buffer', 'out_name': 'joboutput' })

But I can't see the job's output as it's produced-- I only see the first line "Reading from channel output...". Only when I call:

call job_stop(job)

Will I see the rest of the output, which is all written to the buffer. So it appears that the job's output is buffered by the OS before I can see it, and stopping the job causes it to be flushed. Is there a way to have Vim continually update the output buffer, the way it would appear if I ran the same job (i.e. process) in a terminal?

  • 1
    Please provide a minimal working cmd to reproduce your problem.
    – dedowsdi
    Commented Jul 17, 2019 at 0:00

1 Answer 1


This is almost surely happening because the output from cmd is getting buffered when being sent to a pipe, so until you get enough of it (a few kilobytes), Vim won't really receive any.

A very simple fix for this, that will work in most cases, is to have Vim use a pty instead of a pipe to communicate with the external job. The standard library in Linux/Unix will typically set up output to be unbuffered when writing to a terminal, so using a pty is a good fix.

You can do that by including 'pty': 1 as part of the job options.

let job = job_start(cmd, { 'out_io': 'buffer', 'out_name': 'joboutput', 'pty': 1 })

See documentation for job options, which includes:

"pty": 1                Use a pty (pseudo-tty) instead of a pipe when
                        possible.  This is most useful in combination with a
                        terminal window, see terminal.

Alternatively, you can make sure your external cmd will use unbuffered output, for which there are some options depending on what cmd is. If it's a C program, then stdbuf is usually an option, if it's a Python program, then using python -u or setting the PYTHONUNBUFFERED=1 environment variable works. Some of the solutions (such as unbuffer) actually use a pty wrapper. (Search Unix&Linux StackExchange and you'll find tons of answers about buffered output!)

  • 1
    Excellent answer, solved my problem with just the right amount of detail and context. Thank you! Commented Jul 17, 2019 at 21:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.