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As described in a section of Linux Fundamentals page, there are three built-in, Standard Streams, each with a well-defined stream number:

• 0 - standard input
• 1 - standard output
• 2 - standard error

Redirection characters allow you to control the stream input or output

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• redirect standard output to a file, overwriting any exiting contents:
  echo "Output text" > out.txt
echo "Output textMore output" 1> out.txt

• redirect standard output to a file, appending to any exiting contents:
  echo "More Some text" >> out.txt
echo "More text" 1>> out.txt
• redirect standard error output to a file, overwriting any exiting contents:
echo "Error text" 2> ls xxxx 2> err.txt
• redirect standard error to standard output:
  ls xxxx > ls.log 2>&1
• redirect standard output to standard error:
  echo "Output that will go to standard error" 1>&2

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# list 2 files, one that exists and one that does not
ls ~/.profile ~/xxx 

Produces this output:

ls: cannot access 'xxx': No such file or directory
.profile

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We've also added command-line processing and usage support for the new functions.

argument defaulting

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