To redirect input for a Unix command from a file instead of the
terminal, enter the command as:
| % command < infile | Take input from file infile. |
| % command arguments < infile | Take input from file infile. |
Here infile is the file from which the command gets its input, and the command's options and arguments are placed before redirection.
To redirect output generated by a Unix command to a file rather
than the terminal, enter the command as:
| % command > outfile | Place output in file outfile. |
| % command arguments > outfile | Place output in file outfile. |
Here outfile is the file to which the command sends its output.
Consider the grep command. It is used to search a file for a
string and write all lines that contain that string to the
standard output device. For example,
| % grep FORMAT *.f | Search all .f files for word FORMAT. |
will search all files with the suffix .f for the character
string (word) FORMAT and will fill up your terminal screen in
a flash with the file names and lines containing FORMAT.
Or, you can place the screenfuls of output in the file matches
with redirection
| % grep FORMAT *.f >matches | Search, puts finds in matches. |