I/O Redirection
- Redirection refers to changing the shell's normal method of handling standard output (stdout), standard input (stdin) and standard error (stderr) for processes. By default, all of these are from/to your screen.
- All commands expect 3 files to be opened for them when they are invoked:
STDIN - Standard input
STDOUT - standard output
STDERR - Standard error -
The following symbols are used on the shell command line to redirect a
process's stdin, stdout and/or stderr to another location, such as a file
or device.
> - redirect stdout to output(overwrite) >> - append stdout to output < - redirect stdin 2&> - redirect stderr (sh,ksh,bash) >& - redirect stdout and stderr (csh,tcsh)
I/O Redirection Examples
Examples:mail tony < memo - uses the file memo as input to the mail program ls -l > my.directory - redirects output of ls -l command to a file called my.directory. If the file already exists, it is overwritten cat Mail/jsmith >> Oldmail - appends the contents of Mail/jsmith to the file Oldmail (does not overwrite) myprog >& output - redirects stdout and stderr from myprog's execution to a file called output (csh,tcsh) (myprog > out) >& err - redirects stdout from myprog's execution to a file called out and stderr to the file err (csh,tcsh) myprog 2> runtime.errors - redirects stderr from myprog's execution to a file called runtime.errors (sh,ksh,bash) myprog > output 2>& - redirects stderr and stdout from myprog's execution to a file called output (sh,ksh,bash) myprog > out 2> err - redirects stdout from myprog's execution to a file called out and stderr to the file err (sh,ksh,bash)
0 comments:
Post a Comment