Making a case for case statements on Linux

#!/bin/bash

echo -n "enter the number of equal sides that the shape has> "
read numsides

# make sure answer is numeric
re="^[0-9]+$"
if ! [[ $numsides =~ $re ]] ; then
   echo "error: Not a number" >&2; exit 1
fi

if [ $numsides -lt 3 ]; then
    echo "Sorry, but that would NOT be a geometric shape"
elif [ $numsides == 3 ]; then
    echo triangle
elif [ $numsides == 4 ]; then
    echo square or rectangle
elif [ $numsides == 5 ]; then
    echo pentagon 
elif [ $numsides == 6 ]; then
    echo hexagon 
elif [ $numsides == 7 ]; then
    echo heptagon 
elif [ $numsides == 8 ]; then
    echo octagon 
elif [ $numsides == 9 ]; then
    echo nonagon 
elif [ $numsides == 10 ]; then
    echo decagon 
elif [ $numsides == 11 ]; then
    echo hendecagon 
elif [ $numsides == 12 ]; then
    echo dodecagon 
elif [ $numsides -gt 12 ]; then
    echo "Hmm, you’d better ask Google"
fi

Using case statements, on the other hand, makes your code much simpler to put together and much easier to read.

#!/bin/bash

echo -n "enter the number of equal sides that the shape has> "
read numsides

# make sure answer is numeric
re="^[0-9]+$"
if ! [[ $numsides =~ $re ]] ; then
   echo "error: Not a number" >&2; exit 1
fi

case "$numsides" in
    0-2) echo "Sorry, but that would NOT be a geometric shape";;
    3) echo triangle;;
    4) echo square or rectangle;;
    5) echo pentagon;;
    6) echo hexagon;;
    7) echo heptagon;;
    8) echo octogon;;
    9) echo nonagon;;
    10) echo decagon;;
    11) echo hendecagon;;
    12) echo dodecaggon;;
    *) echo "Hmm, you’d better ask Google"
esac

Each segment in the case statement must end with two semicolons. However, you could use multiple commands separated by semicolons and only use the double semicolons at the end od that segment.

Wrap-up

Notice how much easier case commands are to set up and maintain. You can provide any number of possible values at the cost of one line each.