Understanding stdin stdout stderr

stdout stdin stderr
Alex Mollberg picture Alex Mollberg · Jan 28, 2013 · Viewed 19.7k times · Source

I'm trying to understand stdin stdout and stderr.

I see them used in people's code all the time and I can't understand exactly what they are. I am assuming that they have something to do with input/output but have been searching for an explanation online and can't find one. Does anybody know of a good link with an explanation or if it is simple enough to explain it would be a great help to me.

Since I am learning Python 3, examples in that would be helpful.

Answer

Suku picture Suku · Jan 28, 2013 
sys.stdin
sys.stdout
sys.stderr

File objects used by the interpreter for standard input, output and errors:

  • stdin is used for all interactive input (including calls to input());

  • stdout is used for the output of print() and expression statements and for the prompts of input();

  • The interpreter’s own prompts and its error messages go to stderr.

For your more understanding:

>>> import sys
>>> for i in (sys.stdin, sys.stdout, sys.stderr):
...     print i
... 
<open file '<stdin>', mode 'r' at 0x103451150>
<open file '<stdout>', mode 'w' at 0x1034511e0>
<open file '<stderr>', mode 'w' at 0x103451270>

mode r means reading and mode w means writing

Related questions

Confused about stdin, stdout and stderr?

I am rather confused with the purpose of these three files. If my understanding is correct, stdin is the file in which a program writes into its requests to run a task in the process, stdout is the file into …

Read More
Standard input and output units in Fortran 90?

How can I read and write to the standard input, output and error streams stdin, stdout and stderr in Fortran? I've heard writing to stderr, for example, used to be write(5, fmt=...), with 5 the unit for stderr, and I know …

Read More
How can I reinitialize Perl's STDIN/STDOUT/STDERR?

I have a Perl script which forks and daemonizes itself. It's run by cron, so in order to not leave a zombie around, I shut down STDIN,STDOUT, and STDERR: open STDIN, '/dev/null' or die "Can't read /dev/…

Read More