How to use standard files in shell commands
Last revision August 3, 2004
Special characters (metacharacters) typed as part of commands are interpreted
by the shell as instructions to redirect the standard input, output, or error:
<
redirects standard input from an existing file. Usage:
program < infile
The input file must already exist or there will be an error.
>
redirects standard output to a new file. Usage:
program > outfile
A new output file is created; if one already exists with the same name, it is
silently removed first. To prevent this anti-social behavior,
use set noclobber in your .login file (this is the default
setting for new pangea accounts). Then the command will abort rather than over-write
the existing file.
>>
redirects standard output to be appended to an existing file. Usage:
program >> outfile
If the output file does not exist already, you will get an error.
Standard error can not be independently redirected (in the C-shell). It can be
redirected together with the standard output, however. Just add the ampersand
metacharacter
(&)
after the
>
or
>>
that is redirecting the standard output, for example,
>&
or
>>&
You can put both types of redirection together for a command that reads from
standard input and writes to standard output:
program < infile > outfile
