如何获得特定索引处的字符串字符？

Question

I'm trying to write a script where the user enters a number as a parameter and the script calculates the sum of all the digits eg,

    ./myScript 963
    18

So the script takes the string "963" and adds all the characters in the string 9+6+3=18 . I'm thinking I could get the length of the string and use a loop to add all the indexes of the string together but I cannot figure out how to get an index of the string without already knowing the character you're looking for.

I was able to break the string up using the following command,

    echo "963" | fold -w1
    9
    6
    3

But I'm not sure if/how I could pipe | or redirect > the results into a variable and add it to a total each time.

How can I get a character of a string at a particular index?

Update:

Example 1:

$1=59 then the operation is 5+9=14

Example 2:

$1=2222 then the operation is 2+2+2+2=8

All the characters in the string are added to a total sum.

Answer 1

The following script loops through all of the digits in the input string and adds them together:

#!/bin/bash

s="$1"

for ((i=0; i<${#s}; ++i)); do
    ((t+=${s:i:1}))
done

echo "sum of digits: $t"

The syntax ${s:i:1} extracts a substring of length 1 from position i in the string $s .

Output:

$ ./add.sh 963
sum of digits: 18 

If you wanted to continue adding together the digits until there was only one remaining, you could do this instead:

#!/bin/bash

s="$1"

while (( ${#s} > 1 )); do
    t=0
    for ((i=0; i<${#s}; ++i)); do
        ((t+=${s:i:1}))
    done
    echo "iteration $((++n)): $t"
    s=$t
done   
echo "final result: $s"

The outer while loop continues as long as the length of the string is greater than 1. The inner for loop adds together each digit in the string.

Output:

$ ./add.sh 963
iteration 1: 18
iteration 2: 9
final result: 9 

Not that you asked for it but there are many ways to sum all of the digits in a string. Here's another one using Perl:

$ perl -MList::Util=sum -F -anE 'say sum @F' <<<639
18

List::Util is a core module in Perl. The sum subroutine does a reduction sum on a list to produce a single value. -a enables auto-split mode so the input is split into the array @F . -F is used to set the field delimiter (in this case it is blank, so every character counts as a separate field). -n processes every line of input one at a time and -E is used to enter a Perl one-liner but with newer features (such as say ) enabled. say is like print but a newline is added to the output.

If you're not familiar with the <<< syntax, it is equivalent to echo 639 | perl ... echo 639 | perl ... .

Answer 2

Not using string subscription but computing the desired sum:

number=963
sum=0
for d in `echo "$number" | sed 's,\(.\), \1,g'`
do
    sum=$(($sum + $d))
done
echo $sum

Output: 18

Answer 3

I would do this:

num="963"
echo "$num" | grep -o . | paste -sd+ - | bc

#or using your fold
echo "$num" | fold -w1 | paste -sd+ - | bc

both prints

18

Explanation

• the grep -o . return each digit from your number as well as the fold -w1
• the paste -sd+ - merges the lines to one line using the delimiter + - eg create an calculation string like 9+6+3
• the bc does the calculation

if you want script, eg digadd.sh use

grep -o . <<<"$1" | paste -sd+ - | bc

using it

$ bash digadd.sh             #nothing
$ #will return nothing

$ bash digadd.sh 1273617617273450359345873647586378242349239471289638982
268
$

For fun, doing this in loop until the result is only 1 digit

num=12938932923849028940802934092840924
while [[ ${#num} > 1 ]]
do
    echo -n "sum of digits for $num is:"
    num=$(echo "$num" | grep -o . | paste -sd+ - | bc)
    echo $num
done
echo "final result: $num"

prints

sum of digits for 12938932923849028940802934092840924 is:159
sum of digits for 159 is:15
sum of digits for 15 is:6
final result: 6

another fun variant, what will extract all digits from any string is:

grep -oP '\d' <<<"$1" | paste -sd+ - | bc

so using it in the script digadd.sh like

bash digadd.sh 9q6w3

produces

18

The answer for your question in the title: To getting the Nth character from any string you can use

echo "$string:POSITION:length"  #position from 0

eg to get the 1st digit

echo "${num:0:1}"

Answer 4

You can use cut with -c parameter to get character at any position. for example:

echo "963" | cut -c1

Outputs: 9

Answer 5

使用awk ：

awk 'split($0,a,""){for(i in a) sum+=i}END{print sum}' <<<$1

Answer 6

This can be done using substring manipulation (supported by busybox ash, but not posix sh compliant)

#!/bin/ash
i=0
sum=0
while [ $i -lt ${#1} ]; do
  sum=$((sum+${1:i:1}));
  i=$((i+1))
done
echo $sum

If you really must have a posix shell compliant version, you can use:

#!/bin/sh
sum=0
A=$1

while [ ${#B} -lt ${#A} ];do
  B=$B?
done

while [ "$A" ]; do
  B=${B#?*}
  sum=$((sum+${A%$B}))
  A=${A#?*}
done

echo $sum