Page Comparison

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What this section covers

• Standard Unix streams, redirection and piping
• How and why to direct script diagnostic messages to standard error, but function results to standard output
• Argument defaulting
• Automatically creating a log file for a script
• Capturing standard output in a variable using backtick quoting

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Redirection characters allow you to control the stream input or output

• "<" read from
• ">" write to (and it's cousin ">>" append to, when the destination is a file)

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

• redirect standard output to a file, appending to any exiting contents:
  echo "More text" >> out.txt
echo "More text" 1>> out.txt
• redirect standard error output to a file, overwriting any exiting contents:
echo "Error text" 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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For example, here's how to call the step_01.sh script so that its output goes to both the terminal and to a file.

~/workshop/step_01.sh helloWorld My name is Anna | tee step_01.log

See Piping in the Linux Fundamentals page.

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