On Monday, October 28, 2013 6:53:09 PM UTC+11, Alex Kocharin wrote:
>
>
> var fs = require('fs')
> , childProcess = require('child_process')
> , stream = fs.createWriteStream('/tmp/output.log')
> , child = childProcess.spawn('bash', ['-c', 'echo STDOUT; echo STDERR
> >&2; echo DONE;'])
>
> child.stderr.pipe(stream)
> child.stdout.pipe(stream)
>
>
Thanks for the suggestion, although unfortunately I don't think that would
work for my real scenario. I'm spawning long running tasks, which may
outlive the process that spawned them (which is why I'm directing the
output into a file). Presumably these streams would all stop working / die
when my parent process ends.
> On Sunday, October 27, 2013 5:19:50 AM UTC+4, Tim Cuthbertson wrote:
>>
>> I want to spawn a child process and have *all* output go to the same file.
>>
>> I tried this:
>>
>> var fs = require('fs'), childProcess = require('child_process');
>> var output = fs.openSync('/tmp/output.log', 'w');
>> childProcess.spawn('bash', ['-c', 'echo STOUT; echo STDERR >&2; echo
>> DONE;'], {stdio: ['ignore', output, output]});
>>
>> Which presumably provides the same FD for both stdout and stderr in the
>> child process. Looking at the file produced, I get:
>>
>> STOUT
>> DONE
>>
>> stderr is apparently being ignored. Looking at the child_process docs,
>> there's an example that opens *two* versions of the same file (in append
>> mode), and uses this for stdout / stderr. Since I want to truncate the file
>> (not append), I tried:
>>
>> var fs = require('fs'), childProcess = require('child_process');
>> var output = fs.openSync('/tmp/output.log', 'w');
>> var output2 = fs.openSync('/tmp/output.log', 'a');
>> childProcess.spawn('bash', ['-c', 'echo STOUT; echo STDERR >&2; echo
>> DONE;'], {stdio: ['ignore', output, output2]});
>>
>> But it looks like the write stream is not playing nice and is overwriting
>> the other stream's output, as I get:
>>
>> STOUT
>> DONE
>> R
>>
>> So I guess I have to explicitly truncate the file first, then open two
>> append streams to it?
>>
>> fs.closeSync(fs.openSync('/tmp/output.log', 'w'));
>> var output = fs.openSync('/tmp/output.log', 'a');
>> var output2 = fs.openSync('/tmp/output.log', 'a');
>> childProcess.spawn('bash', ['-c', 'echo STOUT; echo STDERR >&2; echo
>> DONE;'], {stdio: ['ignore', output, output2]});
>>
>> Which finally gives me the desired output:
>>
>> STOUT
>> STDERR
>> DONE
>>
>> For kicks, I also tried reusing a single append stream:
>>
>> fs.closeSync(fs.openSync('/tmp/output.log', 'w'));
>> var output = fs.openSync('/tmp/output.log', 'a');
>> childProcess.spawn('bash', ['-c', 'echo STOUT; echo STDERR >&2; echo
>> DONE;'], {stdio: ['ignore', output, output]});
>>
>> But that gave me the same results as my initial attempt (no stderr at
>> all).
>>
>>
>> I guess I've discovered *how* to do this (my third attempt), but that
>> seems pretty ugly. Can anyone suggest a better way? In python, we can
>> explicitly redirect the child's stderr to stdout:
>>
>> output = open('/tmp/output.log', 'w');
>> subprocess.Popen(['bash', '-c', 'echo STOUT; echo STDERR >&2; echo
>> DONE;'], stderr = subprocess.STDOUT)
>>
>> Is there anything similar in nodejs, or am I stuck with explicitly
>> truncating the file, followed by opening two append-mode descriptors?
>>
>> Cheers,
>> - Tim.
>>
>
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