pipeline between 2 programs

[nilamo]

Sounds similar to before. Using stdout=PIPE, you can just read from the process's .stdout file-like attribute. Then just keep looping through the processes until all of the processes .poll() method returns True.

[Skaperen]

here's what i have put together so far:

def run_pipe_line(*a):
    from subprocess import PIPE, Popen
    if len(a) == 1 and isinstance(a[0],(list,tuple)):
        # a list of commands instead of one per arg
        a = a[0]
    l = len(a)
    if l < 1: # if no commands then no results
        return []
    if l < 2: # if just one command then just do it
        p = [Popen(a[0])]
    else:
        for n in range(l):
            if n < 1: # if this is first command
                p = [Popen(a[0],stdout=PIPE)]
            elif n == l-1: # if this is last command
                p.append(Popen(a[l-1],stdin=p[n-1].stdout))
            else:
                p.append(Popen(a[n],stdin=p[n-1].stdout,stdout=PIPE))
    r = []
    for n in range(l): # wait for all and collect results
        r.append(p[n].wait())
    return r

note that it can take either one command per argument or a list of commands as one argument. i like to be flexible like that. i did a little test of it a few minutes ago and it worked both ways, after fixing one bug on line 16 (the 'l-1' was 'l-2').

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one reason i wanted to make this function (after many which i did not do it) is a program i wrote to do time stamps. it would prefix lines read from stdin and print them to stdout. it would also take arguments as a line to print with a time stamp. and it would also accept the "-e" option (or an "e" in the command name alias) to use the arguments as a command to execute and prefix that command's stdout with time stamps on each line. but this was implemented in a hackish way using bash and i wanted to make a cleaner pipeline. but now i realize even that is a bad hack because it runs a 2nd instance of itself. it should just read the executed command in to itself.