Sed's Substitute Command -- Solution

• Motivation -- You often need to update text files.
• The information -- The sed command replaces a regular expression (R.E.) in a text file.
• Positive instance --
  • sed 's/cat/dog/' pets.txt
  • sed 's/[Cc]at/dog/' pets.txt
  • sed 's/cat/dog/g' pets.txt
  • sed 's+cat+dog+' pets.txt
• Critical properties --
  • Non-interactive ("batch") editing.
  • The 'old' text is identified with a regular expression.
  • Regular expressions are a powerful pattern-matching technique.
  • A 'g' after the last delimiter causes replacement to occur on every instance of the R.E.
  • The delimiter doesn't have to be a '/'.
• Negative instance -- If you omit the 'g', only the first occurrance of the R.E. in each line is replaced.
• Teaching questions --
  • Why might you need to update a text file?
  • What tools are available for this purpose?
  • When might you need to edit non-interactively?
  • When might you prefer a delimiter other than '/'?
• Exercising questions --
  • Write the sed command to replace pigs with goats in the pets.txt file.
  • What if the word 'pig' is capitalized?
  • What if it's plural?
• Evaluating questions --
  • Raise your hand if you could use sed to replace 'yellow' with 'purple'.
  • Will you use sed in real life? Why?

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