Python Os.dup2() Method



Python method dup2() duplicates file descriptor FD to fd2, closing the latter first if necessary.

Note − New file description would be assigned only when it is available. In the following example given below, 1000 would be assigned as a duplicate fd in the case when 1000 is available.


Following is the syntax for dup2() method:

os.dup2(fd, fd2);


  • fd - This is the File descriptor to be duplicated.
  • fd2 − This is a Duplicate file descriptor.

Return Value

This method returns a duplicate of file descriptor.


The following example shows the usage of dup2() method.


import os, sys

# Open a file
fd = os.open( "foo.txt", os.O_RDWR'os.O_CREAT )

# Write one string
os.write(fd, "This is test")

# Now duplicate this file descriptor as 1000
fd2 = 1000
os.dup2(fd, fd2);

# Now read this file from the beginning using fd2.
os.lseek(fd2, 0, 0)
str = os.read(fd2, 100)
print "Read String is : ", str

# Close opened file
os.close( fd )

print "Closed the file successfully!!"

When we run the above program, it produces the following result:

Read String is :  This is test
Closed the file successfully!!

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