How to use standard files in shell commands
Last revision August 3, 2004
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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
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