HI,


Could anyone please give me insigt into output redirection .

I execute followu=ing commands

Scenario :

************
$(cat xxx 2>&1)> test

As i understand from the syntax if command errors out then it will place output in the same place where it would had put normal output.

**********
$(cat xxx 3>&2 2>&1 1>&3) > test

But here i m really confused with file descriptor 3.

Could anyone plz explain it ?.........


Looking forward to hear from Linux community.

Thanx well in advance.

Output redirection uses the pipe charactor | which lives above the backslash which is above the return key. (IF that makes sense, it's late and I'm tired.) The > writes the output of the previous command to a file. I'm not sure what using > multiple times in the same command when you don't mean to write multiple files will do. Probably just doesn't work.

Hope that helps....

David

this basically turns 1 and 2 arround: now only error messages are in 'test' and no other output
in bash you have 9 descriptors (and google-ing for descriptors and bash usually gets you some nice tutorials)
1 is reserved for stdout
2 is reserved for stderr
3-9 are not reserved

after (cat xxx 3>&2 2>&1 1>&3) your have 1 = stderr and 2 = stdout, but only outside of the brackets.

2>&1 is about descriptors, not files
| is a pipe and not output redirection
different countries have different keyboards, so generallizing that one key is obove another does not always make sense.

Hi Nathanael,

Thanx alot for ur valuable inputs.

correct me if i m wrong in saying that
1.when we execute command like ..file 2>&1 , it does mean report output & error(if any) in same file .

2.Now here, let me break entire expression in three parts

3>&2 -- Does it mean output value to be placed where error vals r placed?..
2>&1 -- Does it mean error vals to be place where stdout vals r placed?..
1>&3 -- Does it mean stdout vals r placed where out vals r placed i.e. in turn output to be placed where errors are placed ?..

3. What is the significance of File Descriptors i.e. 3-9 in normal sense ?.
How do they act as out/in/error descriptor ?..
or their behaviour depends on the context in which they have been used?..

I may sound sound naive in asking aforesaid questions, but i need clarification.

Looking forward to hear from you.