标准hsdmt/输出重定向：
sandardinputandoutputredirection
theshellandmanyunixcommandstaketheirinputfrom
Sandardinput(stdin )，write output to
标准输出(stdout )，and write error
outputtostandarderror(stderr ).By default，
sandardinputisconnectedtotheterminalkeyboardandstandard
outputanderrortotheterminalscreen。
thewayofindicatinganend-of-fileonthedefaultstandard
input，a terminal，is usually。
Redirection of I/O，for example to a file，is accomplished by
specifyingthedestinationonthecommandlineusinga
redirectionmetacharacterfollowedbythedesire
目的。
c -壳族
someoftheformsofredirectionforthecshellfamilyare :
角色
操作
注册标准
output
redirectstandardoutputandstandarderror
注册标准输入
！
注册标准输出； overwrite file if it exists
！
redirectstandardoutputandstandarderror； overwrite文件if
it exists
redirectstandardoutputtoanothercommand (pipe ) )。
附加标准输出
appendstandardoutputandstandarderror
theformofacommandwithstandardinputandoutputredirection
is:
% command-[ options ] [ arguments ] input file output file
ifyouareusingcshanddonothavethenoclobber
variable set，using and to
redirectoutputwilloverwriteanyexistingfileofthatname。
settingnoclobberpreventsthis.using！
和！ always forces the file to be
overwritten. Use and
到to append output to existing files。
redirectionmayfailundersomecircumstances :1 ) if you have
thevariablenoclobbersetandyouattempttoredirect
outputtoanexistingfilewithoutforcinganoverwrite，2 ) if you
redirectoutputtoafileyoudon ' thavewriteaccessto，and 3) if
you redirect output to a directory。
Examples:
% who names
redirectstandardoutputtoafilename
d names% (pwd; ls -l) > out
Redirect output of both commands to a file named
out
% pwd; ls -l > out
Redirect output of ls command only to a file named
out
Input redirection can be useful, for example, if you have
written a FORTRAN program which expects input from the terminal but
you want it to read from a file. In the following example,
myprog, which was written to read standard input and
write standard output, is redirected to read myin and
write myout:
% myprog < myin > myout
You can suppress redirected output and/or errors by sending it
to the null device, /dev/null. The example
shows redirection of both output and errors:
% who >& /dev/null
To redirect standard error and output to different files, you
can use grouping:
% (cat myfile > myout) >& myerror
The Bourne shell uses a different format for redirection which
includes numbers. The numbers refer to the file descriptor numbers
(0 standard input, 1 standard output, 2 standard error). For
example, 2> redirects file descriptor 2, or
standard error. &n is the syntax for
redirecting to a specific open file. For example
2>&1 redirects 2 (standard error) to 1
(standard output); if 1 has been redirected to a file, 2 goes there
too. Other file descriptor numbers are assigned sequentially to
other open files, or can be explicitly referenced in the shell
scripts. Some of the forms of redirection for the Bourne shell
family are:
Character
Action
>
Redirect standard
output
2>
Redirect standard error
2>&1
Redirect standard error to standard output
<
Redirect standard input
Pipe standard output to another command
>>
Append to standard output
2>&1|
Pipe standard output and standard error to another command
Note that < and > assume
standard input and output, respectively, as the default, so the
numbers 0 and 1 can be left off. The form of a command with
standard input and output redirection is:
$ command -[options] [arguments] < input file> output file
Redirection may fail under some circumstances: 1) if you have
the variable noclobber set and you attempt to redirect
output to an existing file without forcing an overwrite, 2) if you
redirect output to a file you don't have write access to, and 3) if
you redirect output to a directory.
Examples:
$ who > names
Direct standard output to a file named names
$ (pwd; ls -l) > out
Direct output of both commands to a file named
out
$ pwd; ls -l > out
Direct output of ls command only to a file named
out
Input redirection can be useful if you have written a program
which expects input from the terminal and you want to provide it
from a file. In the following example, myprog, which
was written to read standard input and write standard output, is
redirected to read myin and write
myout.
$ myprog < myin > myout
You can suppress redirected output and/or error by sending it to
the null device, /dev/null. The example shows
redirection of standard error only:
$ who 2> /dev/null
To redirect standard error and output to different files (note
that grouping is not necessary in Bourne shell):
$ cat myfile > myout 2> myerror
原文(http://sc.tamu.edu/help/general/unix/redirection.html)