Originally written for and copyright by Information Security Magazine, February 2002 " Windows Security Scripting."

• IO Redirection in Windows NT, 2000, XP, UNIX (sh, bash and variants)
• Running Multiple Commands in Windows NT, 2000, UNIX (sh, bash and variants)

Note: Under DOS & Win9x/ME some of the simple STDOUT redirection and pipes work, but none of the advanced STDERR or multiple command methods are supported.

IO Redirection in Windows NT, 2000, XP, UNIX (sh, bash and variants)

File Descriptors

1	STDOUT
2	STDERR
3+	Additional files as opened by the process

Redirection

cmd1 | cmd1	Pipe STDOUT of cmd1 into STDIN of cmd2
> file	Direct STDOUT to file, overwriting existing contents
>> file	Direct STDOUT to file, appending to existing contents
>| file	Direct STDOUT to file, overwriting even if noclobber is set (UNIX only)
2> file	Direct STDERR to file, overwriting existing contents
2>> file	Direct STDERR to file, appending to existing contents
< file	Get STDIN from file
2>&1	Direct STDERR to the same place as STDOUT
>& file	Direct both STDOUT and STDERR to file
2>&	Duplicate STDOUT to STDERR
echo 'foo' >&2	Send output to STDERR instead of STDOUT

Notes:

1. Numbered file descriptions above may be used arbitrarily.
2. noclobber is a UNIX setting that prevents overwriting (clobbering) existing files by redirection.
3. UNIX /dev/null is equivalent to Windows NUL. Windows NUL is not case sensitive.
4. ^ is the meta-character escape in DOS/Windows, so it may sometimes be necessary to use ^| (e.g. when using egrep in a batch file). You may use ^^ for a litteral ^.

Examples:

dir c:\*.* > myls.txt	Redirect output of ls into myls.txt, overwriting or creating myls.txt if necessary
dir c:\winnt\*.* >> myls.txt	Append more output of ls into myls.txt
noisy_cmd > NUL	Make STDOUT output from noisy_cmd go away
noisy_cmd 2> NUL	Make STDERR output from noisy_cmd go away
noisy_cmd > NUL 2>&1	Make ALL output from noisy_cmd go away
noisy_cmd 2> NUL 1>&2	Make ALL output from noisy_cmd go away
noisy_cmd | more	Pipe noisy_cmd STDOUT into more (or less or whatever)
noisy_cmd 2>&1 | more	Pipe noisy_cmd STDOUT and STDERR into more (this is great for those "net" commands that scroll off the screen when you try to get help)
echo some message 1>&2	Use the echo command to send output to STDERR (it usually goes to STDOUT).

Running Multiple Commands in Windows NT, 2000, UNIX (sh, bash and variants)

cmd1 & cmd2	Run cmd1, then run cmd2
cmd1 ; cmd2	Run cmd1, then run cmd2 (UNIX only)
cmd1 && cmd2	Run cmd1. If it finishes successfully then run cmd2
cmd1 || cmd2	Run cmd1. If it fails then run cmd2