subprocess.check_output failing with error 127

Question

I'm attempting to call an outside program from my python application, but it shows no output and fails with error 127. Executing the command from the command line works fine. (and I am in the correct working directory)

def buildContris (self, startUrl, reportArray):
    urls = []

    for row in reportArray:
        try:
            url = subprocess.check_output(["casperjs", "casper.js", startUrl, row[0]], shell=True)
            print (url)
            urls.append(url)
            break
        except subprocess.CalledProcessError as e:
            print ("Error: " + str(e.returncode) + " Output:" + e.output.decode())          

    return urls

Each loop outputs the following error: (I've also checked e.cmd. It's correct, but long, so I omitted it in this example)

Error: 127 Output: 

SOLUTION:

The following code works

app = subprocess.Popen(["./casperjs/bin/casperjs", "casper.js", startUrl, row[0]], stdout=subprocess.PIPE, stderr=subprocess.PIPE, env = {"PATH" : "/usr/local/bin/:/usr/bin"}, universal_newlines=True)
app.wait()
out, errs = app.communicate()

Answer 1

Try adding the full path to casperjs in your subprocess.check_output() call.

Edit: Answeing your 2nd question. My apologies for the formatting as I'm on iPad. I think you should try Popen instead of check_output so that you can specify environment variables:

p = subprocess.Popen(["/path/to/casperjs", "casper.js", startUrl, row[0]], env={"PATH": "/path/to/phantomjs"})
url, err = p.communicate()

Answer 2

shell=True changes the interpretation of the first argument (args) in check_output() call, from the docs:

On Unix with shell=True, ... If args is a sequence, the first item specifies the command string, and any additional items will be treated as additional arguments to the shell itself. That is to say, Popen does the equivalent of:

Popen(['/bin/sh', '-c', args[0], args[1], ...])

Exit status 127 might mean that the shell haven't found casperjs program or casperjs itself exited with that code.

To fix the code: drop shell=True and specify the full path to the casperjs program e.g.:

url = check_output(["./casperjs", "casper.js", startUrl, row[0]])