CODEWITHSUNDEEP
windowscmdio-redirection
igbgotiz
igbgotiz

Reputation: 942

windows cmd: why does the order in which you specify output redirection matter?

if you do 

ipconfig.exe 1> output.log 2>&1

this will direct all output(both stdout and stderr) to "output.log".

However, if you do (changing the order in which you specify desired redirections)

ipconfig.exe 2>&1 1> output.log

this will not achieve the intended effect of printing both output streams to "output.log" because "stderr" in this case will be printed to the console.

I suspect this has to do with the way "cmd" parses commands that gives different meanings depending on the order in which you specify redirects.

If so, what are the semantic rules and where are they documented?

I reckon this is something worth finding out as it could waste people hours by making them scratching their head trying to figure out why their redirection is not working.

Upvotes: 4

Views: 86

Answers (1)

Mark Setchell
Mark Setchell

Reputation: 207465

The redirections are simply parsed left to right. Initially stdout and stderr are pointing to the console, so when you redirect stderr to where stdout is currently pointing in the second example, you are directing stderr to the console. You then subsequently redirect stdout to a file.

The explanations and examples here are quite good for further reference.

Upvotes: 4

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