Question

This is my code for a bubble sort on n numbers:

#!/bin/bash

echo -n  "Input n, the number of numbers"
read N
declare -a array[N]
echo -e "Input the elements, press enter after each element"
for i in seq 1 $N  
do 
    read array[$i]
done

swap1()
{ # for swapping two numbers, we are employing bubble sort
    local temp = ${array[$1]} 
    array[$1] = ${array[$2]}
    array[$2]=$temp
    return
}

numb_elements=${#array[@]}
let "comparisons = $numb_elements - 1"

count=1

while [ "$comparisons" -gt 0]
do
   index =0

   while[ "$index" -lt "$comparisons" ];do
      if [ ${array[$index]} \> ${array[ 'expr $index + 1']} ]
      then 
         swap1 $index 'expr $index + 1'
      fi
      let "index += 1" # Or, index+=1 on Bash, ver. 2.1 or newer
   done

   let "comparisons -=1"
   echo 
   echo "$count: ${array[@]}
   echo

   let "count +=1"
done
exit 0

I have two problems with this code:

1. the input array just takes 3 numbers
2. and then i get an error on line 42 saying syntax error for the command while do

I have tried while [] ; do, but it doesn’t work.

Its just been a day that i have been trying bash syntax.

Answer 1

You made a series of errors:

• correct spaces are fundamental to shell scripting
• missing “ apices to execute code and get the output
• logic error (starting inserting from the second array element and using it from the first one)
• iterating the wrong number of time for the bubblesort alg

This is your code corrected.

#!/bin/bash

swap1() { # for swapping two numbers, we are employing bubble sort
        local temp=${array[$1]}

        array[$1]=${array[$2]}
        array[$2]=$temp
        return
}


echo -n "Input n, the number of numbers: "

read N
declare -a array[$N]

echo -e "Input the elements, press enter after each element"
for i in `seq 1 $N`
do
        read array[$i]
done

numb_elements=${#array[@]}
#let "comparisons = $numb_elements - 1"
comparisons=$numb_elements
count=1
while [ "$comparisons" -gt 0 ]
do
        index=1
        while [ "$index" -lt "$comparisons" ]
        do
                tmp=`expr $index + 1`
                if [ ${array[$index]} -gt ${array[$tmp]} ]
                then 
                        swap1 $index $tmp
                fi
                let "index += 1" # Or, index+=1 on Bash, ver. 2.1 or newer
        done
        let "comparisons -= 1"
        echo
        echo "$count: ${array[@]}"
        echo
        let "count += 1"
done

exit 0