What I am going to do is to create multiple output steams in a python function, and refer them as 1, 2, 3.....:
In test.py:
def main():
...
print >>fd1, 'words1'
print >>fd2, 'words2'
print >>fd3, 'words3'
...
Redirect it while using:
python test.py 1>1.txt 2>2.txt 3>3.txt
The content of these files:
1.txt -> words1
2.txt -> words2
3.txt -> words3
The question is, how to create those fd1, fd2, fd3?
Added:
I have used this:
outfiles = {}
for _ in range(3):
fd = os.dup(1)
outfiles[fd] = os.fdopen(fd, 'w')
def main():
for no in outfiles:
print >>outfiles[no], "foo"
print >>outfiles[no], outfiles[no].fileno()
But the results depends on how I execute this code:
eg1:
python test.py
foo
3
foo
4
foo
5
eg2:
python test.py 3>log.txt
foo
4
foo
5
foo
6
eg3:
python test.py 1>log.txt
Nothing printed
So I guess, the output is actually 1, and if a file descriptor have already been used in execute (eg:python test.py 3>log.txt), the os.dup(1) won't return it anymore.
On Linux, the file handles that you want exist in /proc/self/fd/. For example:
with open('/proc/self/fd/1', 'w') as fd1, open('/proc/self/fd/2', 'w') as fd2, open('/proc/self/fd/3', 'w') as fd3:
print >>fd1, 'words1'
print >>fd2, 'words2'
print >>fd3, 'words3'
On some other unices, you may find similar file handles under /dev/fd.
Now, you can run your command and verify that the output files are as desired:
$ python test.py 1>1.txt 2>2.txt 3>3.txt
$ cat 1.txt
words1
$ cat 2.txt
words2
$ cat 3.txt
words3
The OS places limits on the maximum number of open file descriptors that a process may have. For a discussion of this see "Limits on the number of file descriptors".
When using bash's numbered file descriptors, the restrictions are much tighter. Under bash, only file descriptors up to 9 are reserved for the user. The use of higher numbers may cause conflict with bash's internal use. From man bash:
Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally.
If, as per the comments, you want to assign hundreds of file descriptors, then don't use shell redirection or the numbered descriptors in /proc/self/fd. Instead, use python's open command, e.g. open('255.txt', 'w') directly on each output file that you want.