How to convert text files to all upper or lower case

How can you convert a text file to all lower case or all upper case?

As usual, in Linux, there are more than 1 way to accomplish a task.

To convert a file (input.txt) to all lower case (output.txt), choose any ONE of the following:

• dd
  

  $ dd if=input.txt of=output.txt conv=lcase

  
  
• tr
  

  $ tr '[:upper:]' '[:lower:]' < input.txt > output.txt

  
  
• awk
  

  $ awk '{ print tolower($0) }' input.txt > output.txt

  
  
• perl
  

  $ perl -pe '$_= lc($_)' input.txt > output.txt

  
  
• sed
  

  $ sed -e 's/\(.*\)/\L\1/' input.txt > output.txt

  
  We use the backreference \1 to refer to the entire line and the \L to convert to lower case.
  

To convert a file (input.txt) to all upper case (output.txt):

• dd
  

  $ dd if=input.txt of=output.txt conv=ucase

  
  
• tr
  

  $ tr '[:lower:]' '[:upper:]' < input.txt > output.txt

  
  
• awk
  

  $ awk '{ print toupper($0) }' input.txt > output.txt

  
  
• perl
  

  $ perl -pe '$_= uc($_)' input.txt > output.txt

  
  
• sed
  

  $ sed -e 's/\(.*\)/\U\1/' input.txt > output.txt