In Linux shell script how do I print the largest and smallest values of an array?

Question

I don’t really understand much about arrays, but I need to know how to find and print the largest and smallest values of an array. The array is predefined by a read command, and the user will be prompted to enter n amount of integers.

How would I assign the read input to an array and find and display the largest and smallest values of the array?

Is there a way to test the array elements to see if they are all integers?

#!/bin/bash

read -a integers

biggest=${integers[0]}
smallest=${integers[0]}

for i in ${integers[@]}
do
     if [[ $i -gt $biggest ]]
     then
        biggest="$i"
     fi

     if [[ $i -lt $smallest ]]
     then
        smallest="$i"
     fi
done

echo "The largest number is $biggest"
echo "The smallest number is $smallest"

Answer 1

You could sort the array, then the first and last elements will be your min and max values:

sorted=($(IFS=$'\n'; sort -n <<< "${integers[*]}"))
echo "The largest number is ${sorted[-1]}"
echo "The smallest number is ${sorted[0]}"

To test if an array is all integers, you could use the following bash function:

is_int_array() {
    for e in "$@"; do
        [[ "$e" =~ ^-?[0-9]+$ ]] || return 1
    done
    return 0
}

To use the function:

is_int_array "${integers[@]}" && echo 'is int array' || echo 'not all integers'
is int array

is_int_array 'a' 1 2 3  && echo 'is int array' || echo 'not all integers'
not all integers

is_int_array 1 2 3 -4 && echo 'is int array' || echo 'not all integers'
is int array

Answer 2

Here is the code to find maximum and minimum values from an array of n integers.

#author@Pratham
declare -a arr
echo "How many numbers you want to enter?"
read n
echo "Enter the Array Elements"
for(( i=0 ; i<$n ; i++))
do
    read array_elements
    arr[$i]="$array_elements"
done
echo "The Array Elements are :"
echo -e "${arr[@]}"
max=${arr[0]}
min=${arr[0]}
for i in "${arr[@]}"
do
    if [[ $i -gt $max ]];
    then
        max=$i
    fi
    if [[ $i -lt $min ]];
    then
        min=$i
    fi
done
echo "Maximum element in the array is: $max"
echo "Manimum element in the array is: $min"

Answer 3

Try this if you need to compare (signed or not) INTegers :

#!/bin/bash

arr=( -10 1 2 3 4 5 )

min=0 max=0

for i in ${arr[@]}; do
    (( $i > max || max == 0)) && max=$i
    (( $i < min || min == 0)) && min=$i
done

echo "min=$min
max=$max"

OUTPUT

min=-10
max=5

EXPLANATIONS

• arr=( ) is the declaration of the array
• ((...)) is an arithmetic command, which returns an exit status of 0 if the expression is nonzero, or 1 if the expression is zero. Also used as a synonym for "let", if side effects (assignments) are needed. See http://mywiki.wooledge.org/ArithmeticExpression
• [[ is a bash keyword similar to (but more powerful than) the [ command. See http://mywiki.wooledge.org/BashFAQ/031 and http://mywiki.wooledge.org/BashGuide/TestsAndConditionals Unless you're writing for POSIX sh, we recommend [[
• foo || bar runs bar when foo fails: [[ -d $foo ]] || { echo 'ohNoes!' >&2; exit 1; }
• cmd1 && cmd2 : cmd1 is executed, and then if its exit status was 0 (true), cmd2 is executed. See http://mywiki.wooledge.org/BashGuide/TestsAndConditionals

Answer 4

A funny way using sort:

if you have an array of integers, you can use sort to sort it, then select the first and last elements to have the min and max elements, as in:

{ read min; max=$(tail -n1); } < <(printf "%s\n" "${array[@]}" | sort -n)

So if you want to prompt user for say 10 integers, check that the user entered integers and then sort them, you could do:

#!/bin/bash

n=10
array=()

while ((n));do
   read -p "[$n] Give me an integer: " i
   [[ $i =~ ^[+-]?[[:digit:]]+$ ]] || continue
   array+=($i)
   ((--n))
done

# Sort the array:
{ read min; max=$(tail -n1); } < <(printf "%s\n" "${array[@]}" | sort -n)
# print min and max elements:
echo "min=$min"
echo "max=$max"

Answer 5

The general idea is to iterate through the array once and keep track of what the max and min seen so far at each step.

Some comments and explanations in-line (prefixed by #)

# This is how to declare / initialize an array:
arrayName=(1 2 3 4 5 6 7)

# Use choose first element of array as initial values for min/max;
# (Defensive programming) - this is a language-agnostic 'gotcha' when
# finding min/max ;)
max=${arrayName[0]}
min=${arrayName[0]}

# Loop through all elements in the array
for i in "${arrayName[@]}"
do
    # Update max if applicable
    if [[ "$i" -gt "$max" ]]; then
        max="$i"
    fi

    # Update min if applicable
    if [[ "$i" -lt "$min" ]]; then
        min="$i"
    fi
done

# Output results:
echo "Max is: $max"
echo "Min is: $min"