CSC%204630

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CSC 4630

• Meeting 6
• February 5, 2007

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Issues from the Quiz

• Text files and wc
• File contains decimal digits, one per line. What
  do we expect from wc?
• File contains two lines, the first with the 26
  upper case characters, the second with the 26
  lower case characters. What do we expect from
  wc?
• Now, wc numbers? wc chars?

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Issues from Quiz (2)

• grep
• Matching is a binary operation on the lines of a
  file.
• cat (grep s file) (grep v s file) lt-gt file
• Two negatives lead to confusion, but
• grep s file is not a negative match. It asks
  for all lines that match some character that is
  not is s
• grep a-c file asks for all lines that contain
  some character that is not an a, nor a b, nor a
  c. So it gets cat but not cab

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More on grep

• grep A-Z file gets ?
• grep A-Za-z0-9 file gets ?
• grep a-z file gets ?
• grep aeiou file gets ?
• grep 5-9 numbers wc produces ?

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More on grep

• Try grep v 5-9 numbers
• What happened
• In words,
• grep v s file gives all lines in the file
  that dont contain a character that is not
  mentioned in s. Hence, all lines in the file
  that contain only mentioned characters.