In addition to the let command, one may use the (( )) syntax to enforce an arithmetic context. If there is a $ (dollar sign) before the parentheses, then a substitution is performed (more on this below). White space is allowed inside (( )) with much greater leniency than with normal assignments, and variables inside (( )) don't require $ (because string literals aren't allowed).

let WC=$(sudo wc -l $MAIN_FILE  | cut -d" " -f1 )                                                                
((WC=$WC - 1 ))                                                                                                  
echo $WC         

  #!/bin/bash          
          echo Hello World 

Ctrl + E: Go to the end of the line you are currently typing on
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Ctrl + F: Forward one character.
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Ctrl + B: Backward one character.
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Meta + F: Move cursor forward one word on the current line
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Meta + B: Move cursor backward one word on the current line
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Ctrl + P: Previous command entered in history
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Ctrl + N: Next command entered in history
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Ctrl + L: Clears the screen, similar to the clear command
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Ctrl + U: Clears the line before the cursor position. If you are at the end of the line, clears the entire line.
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Ctrl + H: Same as backspace
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Ctrl + R: Lets you search through previously used commands
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Ctrl + C: Kill whatever you are running
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Ctrl + D: Exit the current shell
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Ctrl + Z: Puts whatever you are running into a suspended background process. fg restores it.
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Ctrl + W: Delete the word before the cursor
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Ctrl + K: Kill the line after the cursor
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Ctrl + Y: Yank from the kill ring

$ echo `hostname` | sed 's/ip/foo/g'