5.1.2.3. Combining redirections

The following example combines input and output redirection. The file text.txt is first checked for spelling mistakes, and the output is redirected to an error log file:

spell < text.txt > error.log

The following command lists all commands that you can issue to examine another file when using less:

mike:~> less --help | grep -i examine
  :e [file]      Examine a new file.
  :n          *  Examine the (N-th) next file from the command line.
  :p          *  Examine the (N-th) previous file from the command line.
  :x          *  Examine the first (or N-th) file from the command line.

The -i option is used for case-insensitive searches - remember that UNIX systems are very case-sensitive.

If you want to save output of this command for future reference, redirect the output to a file:

mike:~> less --help | grep -i examine > examine-files-in-less

mike:~> cat examine-files-in-less
  :e [file]      Examine a new file.
  :n          *  Examine the (N-th) next file from the command line.
  :p          *  Examine the (N-th) previous file from the command line.
  :x          *  Examine the first (or N-th) file from the command line.

Output of one command can be piped into another command virtually as many times as you want, just as long as these commands would normally read input from standard input and write output to the standard output. Sometimes they don't, but then there may be special options that instruct these commands to behave according to the standard definitions; so read the documentation (man and Info pages) of the commands you use if you should encounter errors.

Again, make sure you don't use names of existing files that you still need. Redirecting output to existing files will replace the content of those files.