Shell Script to Convert a File Content to Lower Case or Upper Case

Here we are going to see how to convert a file to lower case or upper case as specified by the user. We are going to write a  POSIX  compatible shell script which is going to give us the desired output after input of files such as sample.txt, a text file with a combination of lowercase, uppercase, digits and special character

Example:

File Content

this is lowercase

THIS IS UPPERCASE

$P3C14L C#4R4CT3R$

1234567890

OUTPUT

Uppercase

THIS IS LOWERCASE

THIS IS UPPERCASE

$P3C14L C#4R4CT3R$

1234567890

Lowercase

this is lowercase

this is uppercase

$p3c14l c#4r4ct3r$

1234567890

Approach:

• Ask User Choice if they want to convert from Uppercase to Lowercase or vice-versa
• Read the choice
• Get into the Switch case depending on the choice. while exiting if the choice is none of the above-mentioned.
• Asking user for the filename
• Checking if file exists, if not then exit with error code 1, otherwise continue
• Translating the file content as per the previous selected user choice and printing the output by the use of tr command.
• End of Script

Shell Script 

#!/bin/sh
# shebang to specify that this is an shell script

# Function to get File
getFile(){
    # Reading txtFileName to convert it's content
    echo -n "Enter File Name:"
    read txtFileName
    # Checking if file exist
    if [ ! -f $txtFileName ]; then
        echo "File Name $txtFileName does not exists."
        exit 1
    fi
}

clear
  echo "1. Uppercase to Lowercase "
  echo "2. Lowercase to Uppercase"
  echo "3. Exit"
  echo -n "Enter your Choice(1-3):"
  read Ch

  case "$Ch" in
    1) 
      # Function Call to get File 
      getFile    
      # Converting to lower case if user choose 1     
      echo "Converting Upper-case to Lower-Case "
      tr '[A-Z]' '[a-z]' <$txtFileName
    ;;

    2)
      # Function Call to get File 
      getFile
      # Converting to upper case if user cho0se 2
      echo "Converting Lower-Case to Upper-Case "
      tr '[a-z]' '[A-Z]' <$txtFileName
    ;;
    

    *) # exiting for all other cases
        echo "Exiting..."
        exit
    ;;
  esac

Output:

Showcasing content of sample text file with cat command and modifying our script by making it executable with chmod command.

Conversion Input and Output

Running on non-existing files