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关于Window的Dos Batch 文件编写的常识
Redirect "all" output to a single file:
Run:
test.bat > test.txt 2>&1
and you‘ll get this text on screen (we‘ll never get rid of this line on screen, as it is sent to the Console and cannot be redirected):
This text goes to the Console
You should also get a file named test.txt with the following content:
This text goes to Standard Output This text goes to Standard Error
Note: The commands
test.bat > test.txt 2>&1
test.bat 1> test.txt 2>&1
test.bat 2> test.txt 1>&2
all give identical results.
Redirect errors to a separate error log file:
Run:
test.bat > testlog.txt 2> testerrors.txt
and you‘ll get this text on screen (we‘ll never get rid of this line on screen, as it is sent to the Console and cannot be redirected):
This text goes to the Console
You should also get a file named testlog.txt with the following content:
This text goes to Standard Output
and another file named testerrors.txt with the following content:
This text goes to Standard Error
Some "best practices" when using redirection in batch files:
Use
>filename.txt 2>&1
to merge Standard Output and Standard Error and redirect them together to a single file.
Make sure you place the redirection "commands" in this order.Use
>logfile.txt 2>errorlog.txt
to redirect success and error messages to separate log files.Use
>CON
to send text to the screen, no matter what, even if the batch file‘s output is redirected.
This could be useful when prompting for input even if the batch file‘s output is being redirected to a file.Use
1>&2
to send text to Standard Error.
This can be useful for error messages.It‘s ok to use spaces in redirection commands. Note however, that a space between an ECHO command and a
>
will be redirected too.DIR>filename.txt
andDIR > filename.txt
are identical,ECHO Hello world>filename.txt
andECHO Hello world > filename.txt
are not, even though they are both valid.
It is not ok to use spaces in>>
or2>
or2>&1
or1>&2
(before or after is ok).In Windows NT 4, early Windows 2000 versions, and OS/2 there used to be some ambiguity with ECHOed lines ending with a 1 or 2, immediately followed by a
>
:ECHO Hello world2>file.txt
would result in an empty file file.txt and the textHello world
(without the trailing "2") on screen (CMD.EXE would interpret it asECHO Hello world 2>file.txt
).
In Windows XP the result is no text on screen and file.txt containing the lineHello world2
, including the trailing "2" (CMD.EXE interprets it asECHO Hello world2 >file.txt
).
To prevent this ambiguity, either use parentheses or insert an extra space yourself:ECHO Hello World2 >file.txt
(ECHO Hello World2)>file.txt"Merging" Standard Output and Standard Error with
2>&1
can also be used to pipe a command‘s output to another command‘s Standard Input:somecommand 2>&1 | someothercommand