Tukukkk

I have a file called file.txt which has some random numbers from 1 to 100. So a script reads the file and executes a bunch of commands and print some statements.

One way of achieving the result could be something like these but having 100 if and elif statement in a script doesn't look so nice.

for i in `cat file.txt`; do

  echo "Displaying" $i

    if [[ $i = 1 ]]; then

        echo "blah blah blah for" $i

        command1

        command2

    elif [[ $i = 2 ]]; then

        echo "blah blah blah for" $i

        command3

        command4

        command5

    elif [[ $i = 3 ]]; then

        echo "blah blah blah for" $i

        command6

        command7

    elif [[ $i = 4 ]]; then

        echo "blah blah blah for" $i

        command8

        command9

        command10

    elif [[ $i = 5 ]]; then

        echo "blah blah blah for" $i

        command11

        command12

        command13

        command14

    elif [[ $i = 6 ]]; then

        echo "blah blah blah for" $i

        command15



        ....

        ....

        ....

        ....

        ....

        ....

    elif [[ $i = 99 ]]; then

        echo "blah blah blah for" $i

        command310

        command311

        command312

        command313

        command314

    elif [[ $i = 100 ]]; then

        echo "blah blah blah for" $i

        command315

    fi

done

Is there any better or smarter way to do these on bash

Classic case of case:

case "$i" in

    1)

        echo "blah blah blah for" $i

        command1

        command2

        ;;

    […]

    *)

        echo "Unhandled value $i" >&2

        exit 2

esac

In addition to this:

• 
  Use a while loop to process lines


• Use More Quotes™

My suggestion would be to make use of a case statement. It is the bash version of what is known in programming as the switch statement. They are generally faster then an if-then-else statement as they are most likely implemented with a lookup table or hash-list.

Additionally, an optimized implementation may execute much faster than the alternative, because it is often implemented by using an indexed branch table. For example, deciding program flow based on a single character's value, if correctly implemented, is vastly more efficient than the alternative, reducing instruction path lengths considerably. When implemented as such, a switch statement essentially becomes a perfect hash.

source: Wikipedia

An interesting comparison can be found here: Which is faster of two case or if?

To address your code, you're loop of the form

for i in $(cat file); do

  ...

done

should be rewritten. As you read the file word-by-word, you should write something like:

while read -r line; do

   for i in $line; do

     ...

   done

done < file

You're if-then-else is then rewritten as:

case "$i" in

   1) command1; command2; command3 ;;

   2) command4; command5; command6 ;;

   ...

   100) command315; command316;;

esac