bash: expecting number addition with +=. Not exactly sure if the operand is a number

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up vote
2
down vote

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I am trying to detect armstrong numbers with this code:



declare -i INPUT=$1


arr=($(fold -w1 <<< "$INPUT"))
for index in "$!arr[@]"
do
armstrong_sum+=$(($arr[index]**$#arr[@]))
done


echo "$armstrong_sum"


Commands to run the code: ./armstrong_sum 9, armstrong_sum 10 and ./armstrong_sum 153



Output: 9, 10 and 112527



Expected output: 9, 1 and 153



An armstrong number is a number that is the sum of its own digits each raised to the power of number of digits



More importantly I want to be able to debug the script myself. Not exactly sure how one debugs in bash. Like get type of operand and see pause iteration at each step










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  • your expected output doesnt make sense - by your own definition 153 should return 729
    – Steven Penny
    Dec 7 at 3:46











  • 1^3 + 5^3 + 3^3 = 153. This my expected output, i.e an armstrong number
    – HarshvardhanSharma
    Dec 7 at 3:50










  • Your second question (the bold part) already has an answer, easily found by searching: unix.stackexchange.com/questions/155551/…
    – JigglyNaga
    Dec 7 at 9:24














up vote
2
down vote

favorite












I am trying to detect armstrong numbers with this code:



declare -i INPUT=$1


arr=($(fold -w1 <<< "$INPUT"))
for index in "$!arr[@]"
do
armstrong_sum+=$(($arr[index]**$#arr[@]))
done


echo "$armstrong_sum"


Commands to run the code: ./armstrong_sum 9, armstrong_sum 10 and ./armstrong_sum 153



Output: 9, 10 and 112527



Expected output: 9, 1 and 153



An armstrong number is a number that is the sum of its own digits each raised to the power of number of digits



More importantly I want to be able to debug the script myself. Not exactly sure how one debugs in bash. Like get type of operand and see pause iteration at each step










share|improve this question























  • your expected output doesnt make sense - by your own definition 153 should return 729
    – Steven Penny
    Dec 7 at 3:46











  • 1^3 + 5^3 + 3^3 = 153. This my expected output, i.e an armstrong number
    – HarshvardhanSharma
    Dec 7 at 3:50










  • Your second question (the bold part) already has an answer, easily found by searching: unix.stackexchange.com/questions/155551/…
    – JigglyNaga
    Dec 7 at 9:24












up vote
2
down vote

favorite









up vote
2
down vote

favorite











I am trying to detect armstrong numbers with this code:



declare -i INPUT=$1


arr=($(fold -w1 <<< "$INPUT"))
for index in "$!arr[@]"
do
armstrong_sum+=$(($arr[index]**$#arr[@]))
done


echo "$armstrong_sum"


Commands to run the code: ./armstrong_sum 9, armstrong_sum 10 and ./armstrong_sum 153



Output: 9, 10 and 112527



Expected output: 9, 1 and 153



An armstrong number is a number that is the sum of its own digits each raised to the power of number of digits



More importantly I want to be able to debug the script myself. Not exactly sure how one debugs in bash. Like get type of operand and see pause iteration at each step










share|improve this question















I am trying to detect armstrong numbers with this code:



declare -i INPUT=$1


arr=($(fold -w1 <<< "$INPUT"))
for index in "$!arr[@]"
do
armstrong_sum+=$(($arr[index]**$#arr[@]))
done


echo "$armstrong_sum"


Commands to run the code: ./armstrong_sum 9, armstrong_sum 10 and ./armstrong_sum 153



Output: 9, 10 and 112527



Expected output: 9, 1 and 153



An armstrong number is a number that is the sum of its own digits each raised to the power of number of digits



More importantly I want to be able to debug the script myself. Not exactly sure how one debugs in bash. Like get type of operand and see pause iteration at each step







bash






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share|improve this question








edited Dec 7 at 3:59

























asked Dec 7 at 3:30









HarshvardhanSharma

776




776











  • your expected output doesnt make sense - by your own definition 153 should return 729
    – Steven Penny
    Dec 7 at 3:46











  • 1^3 + 5^3 + 3^3 = 153. This my expected output, i.e an armstrong number
    – HarshvardhanSharma
    Dec 7 at 3:50










  • Your second question (the bold part) already has an answer, easily found by searching: unix.stackexchange.com/questions/155551/…
    – JigglyNaga
    Dec 7 at 9:24
















  • your expected output doesnt make sense - by your own definition 153 should return 729
    – Steven Penny
    Dec 7 at 3:46











  • 1^3 + 5^3 + 3^3 = 153. This my expected output, i.e an armstrong number
    – HarshvardhanSharma
    Dec 7 at 3:50










  • Your second question (the bold part) already has an answer, easily found by searching: unix.stackexchange.com/questions/155551/…
    – JigglyNaga
    Dec 7 at 9:24















your expected output doesnt make sense - by your own definition 153 should return 729
– Steven Penny
Dec 7 at 3:46





your expected output doesnt make sense - by your own definition 153 should return 729
– Steven Penny
Dec 7 at 3:46













1^3 + 5^3 + 3^3 = 153. This my expected output, i.e an armstrong number
– HarshvardhanSharma
Dec 7 at 3:50




1^3 + 5^3 + 3^3 = 153. This my expected output, i.e an armstrong number
– HarshvardhanSharma
Dec 7 at 3:50












Your second question (the bold part) already has an answer, easily found by searching: unix.stackexchange.com/questions/155551/…
– JigglyNaga
Dec 7 at 9:24




Your second question (the bold part) already has an answer, easily found by searching: unix.stackexchange.com/questions/155551/…
– JigglyNaga
Dec 7 at 9:24










2 Answers
2






active

oldest

votes

















up vote
2
down vote



accepted










As noted in man bash (emphasis mine)




When += is applied to a variable for which the
integer attribute has been set, value is evaluated as an arithmetic
expression and added to the variable's current value, which is also
evaluated.
When += is applied to an array variable using compound
assignment (see Arrays below), the variable's value is not unset (as it
is when using =), and new values are appended to the array beginning at
one greater than the array's maximum index (for indexed arrays) or
added as additional key-value pairs in an associative array. When
applied to a string-valued variable, value is expanded and appended to
the variable's value.




You are clearly getting the latter, i.e.



1 + 125 + 27 = 112527


So you have a couple of options - either declare armstrong_sum as integer



#!/bin/bash

declare -i INPUT=$1
declare -i armstrong_sum=0

arr=($(fold -w1 <<< "$INPUT"))
for index in "$!arr[@]"
do
armstrong_sum+=$(( $arr[index]**$#arr[@] ))
done


echo "$armstrong_sum"


or ensure arithmetic evaluation by surrounding the whole expression in (( and )) i.e.



(( armstrong_sum += $arr[index]**$#arr[@] ))





share|improve this answer



























    up vote
    0
    down vote













    Use https://www.shellcheck.net (I use it as syntactic vim plugin making a crude IDE)



    I'd go with this;



    #!/bin/bash

    P="$(echo -n "$1" | wc -c)"
    SUM=0;
    for X in $(echo "$1" | fold -w 1) ; do
    SUM=$(echo "$SUM+($X^$P)" | bc );
    done
    echo "$SUM"


    It's not "pure" bash but I find the power of bash is the wide selection of tools, and prioritizing legibility.



    for stack traces if you add the following to the top of all your scripts it will inform you of errors;



    set -e
    trap 'echo "ERROR: $BASH_SOURCE:$LINENO $BASH_COMMAND" >&2' ERR


    it will stop the script on the error line, make output like



    test.sh: line 7: no: command not found
    ERROR: test.sh:7 no + 5


    instead of (potentially silently) ignoring errors.
    Use -x for debugging;



    bash -x armstrong.sh 222
    ++ echo -n 222
    ++ wc -c
    + P=3
    + SUM=0
    ++ fold -w 1
    ++ echo 222
    + for X in $(echo "$1" | fold -w 1)
    ++ echo '0+(2^3)'
    ++ bc
    + SUM=8
    + for X in $(echo "$1" | fold -w 1)
    ++ echo '8+(2^3)'
    ++ bc
    + SUM=16
    + for X in $(echo "$1" | fold -w 1)
    ++ echo '16+(2^3)'
    ++ bc
    + SUM=24
    + echo 24
    24





    share|improve this answer






















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      2 Answers
      2






      active

      oldest

      votes








      2 Answers
      2






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes








      up vote
      2
      down vote



      accepted










      As noted in man bash (emphasis mine)




      When += is applied to a variable for which the
      integer attribute has been set, value is evaluated as an arithmetic
      expression and added to the variable's current value, which is also
      evaluated.
      When += is applied to an array variable using compound
      assignment (see Arrays below), the variable's value is not unset (as it
      is when using =), and new values are appended to the array beginning at
      one greater than the array's maximum index (for indexed arrays) or
      added as additional key-value pairs in an associative array. When
      applied to a string-valued variable, value is expanded and appended to
      the variable's value.




      You are clearly getting the latter, i.e.



      1 + 125 + 27 = 112527


      So you have a couple of options - either declare armstrong_sum as integer



      #!/bin/bash

      declare -i INPUT=$1
      declare -i armstrong_sum=0

      arr=($(fold -w1 <<< "$INPUT"))
      for index in "$!arr[@]"
      do
      armstrong_sum+=$(( $arr[index]**$#arr[@] ))
      done


      echo "$armstrong_sum"


      or ensure arithmetic evaluation by surrounding the whole expression in (( and )) i.e.



      (( armstrong_sum += $arr[index]**$#arr[@] ))





      share|improve this answer
























        up vote
        2
        down vote



        accepted










        As noted in man bash (emphasis mine)




        When += is applied to a variable for which the
        integer attribute has been set, value is evaluated as an arithmetic
        expression and added to the variable's current value, which is also
        evaluated.
        When += is applied to an array variable using compound
        assignment (see Arrays below), the variable's value is not unset (as it
        is when using =), and new values are appended to the array beginning at
        one greater than the array's maximum index (for indexed arrays) or
        added as additional key-value pairs in an associative array. When
        applied to a string-valued variable, value is expanded and appended to
        the variable's value.




        You are clearly getting the latter, i.e.



        1 + 125 + 27 = 112527


        So you have a couple of options - either declare armstrong_sum as integer



        #!/bin/bash

        declare -i INPUT=$1
        declare -i armstrong_sum=0

        arr=($(fold -w1 <<< "$INPUT"))
        for index in "$!arr[@]"
        do
        armstrong_sum+=$(( $arr[index]**$#arr[@] ))
        done


        echo "$armstrong_sum"


        or ensure arithmetic evaluation by surrounding the whole expression in (( and )) i.e.



        (( armstrong_sum += $arr[index]**$#arr[@] ))





        share|improve this answer






















          up vote
          2
          down vote



          accepted







          up vote
          2
          down vote



          accepted






          As noted in man bash (emphasis mine)




          When += is applied to a variable for which the
          integer attribute has been set, value is evaluated as an arithmetic
          expression and added to the variable's current value, which is also
          evaluated.
          When += is applied to an array variable using compound
          assignment (see Arrays below), the variable's value is not unset (as it
          is when using =), and new values are appended to the array beginning at
          one greater than the array's maximum index (for indexed arrays) or
          added as additional key-value pairs in an associative array. When
          applied to a string-valued variable, value is expanded and appended to
          the variable's value.




          You are clearly getting the latter, i.e.



          1 + 125 + 27 = 112527


          So you have a couple of options - either declare armstrong_sum as integer



          #!/bin/bash

          declare -i INPUT=$1
          declare -i armstrong_sum=0

          arr=($(fold -w1 <<< "$INPUT"))
          for index in "$!arr[@]"
          do
          armstrong_sum+=$(( $arr[index]**$#arr[@] ))
          done


          echo "$armstrong_sum"


          or ensure arithmetic evaluation by surrounding the whole expression in (( and )) i.e.



          (( armstrong_sum += $arr[index]**$#arr[@] ))





          share|improve this answer












          As noted in man bash (emphasis mine)




          When += is applied to a variable for which the
          integer attribute has been set, value is evaluated as an arithmetic
          expression and added to the variable's current value, which is also
          evaluated.
          When += is applied to an array variable using compound
          assignment (see Arrays below), the variable's value is not unset (as it
          is when using =), and new values are appended to the array beginning at
          one greater than the array's maximum index (for indexed arrays) or
          added as additional key-value pairs in an associative array. When
          applied to a string-valued variable, value is expanded and appended to
          the variable's value.




          You are clearly getting the latter, i.e.



          1 + 125 + 27 = 112527


          So you have a couple of options - either declare armstrong_sum as integer



          #!/bin/bash

          declare -i INPUT=$1
          declare -i armstrong_sum=0

          arr=($(fold -w1 <<< "$INPUT"))
          for index in "$!arr[@]"
          do
          armstrong_sum+=$(( $arr[index]**$#arr[@] ))
          done


          echo "$armstrong_sum"


          or ensure arithmetic evaluation by surrounding the whole expression in (( and )) i.e.



          (( armstrong_sum += $arr[index]**$#arr[@] ))






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Dec 7 at 4:21









          steeldriver

          34.1k34983




          34.1k34983






















              up vote
              0
              down vote













              Use https://www.shellcheck.net (I use it as syntactic vim plugin making a crude IDE)



              I'd go with this;



              #!/bin/bash

              P="$(echo -n "$1" | wc -c)"
              SUM=0;
              for X in $(echo "$1" | fold -w 1) ; do
              SUM=$(echo "$SUM+($X^$P)" | bc );
              done
              echo "$SUM"


              It's not "pure" bash but I find the power of bash is the wide selection of tools, and prioritizing legibility.



              for stack traces if you add the following to the top of all your scripts it will inform you of errors;



              set -e
              trap 'echo "ERROR: $BASH_SOURCE:$LINENO $BASH_COMMAND" >&2' ERR


              it will stop the script on the error line, make output like



              test.sh: line 7: no: command not found
              ERROR: test.sh:7 no + 5


              instead of (potentially silently) ignoring errors.
              Use -x for debugging;



              bash -x armstrong.sh 222
              ++ echo -n 222
              ++ wc -c
              + P=3
              + SUM=0
              ++ fold -w 1
              ++ echo 222
              + for X in $(echo "$1" | fold -w 1)
              ++ echo '0+(2^3)'
              ++ bc
              + SUM=8
              + for X in $(echo "$1" | fold -w 1)
              ++ echo '8+(2^3)'
              ++ bc
              + SUM=16
              + for X in $(echo "$1" | fold -w 1)
              ++ echo '16+(2^3)'
              ++ bc
              + SUM=24
              + echo 24
              24





              share|improve this answer


























                up vote
                0
                down vote













                Use https://www.shellcheck.net (I use it as syntactic vim plugin making a crude IDE)



                I'd go with this;



                #!/bin/bash

                P="$(echo -n "$1" | wc -c)"
                SUM=0;
                for X in $(echo "$1" | fold -w 1) ; do
                SUM=$(echo "$SUM+($X^$P)" | bc );
                done
                echo "$SUM"


                It's not "pure" bash but I find the power of bash is the wide selection of tools, and prioritizing legibility.



                for stack traces if you add the following to the top of all your scripts it will inform you of errors;



                set -e
                trap 'echo "ERROR: $BASH_SOURCE:$LINENO $BASH_COMMAND" >&2' ERR


                it will stop the script on the error line, make output like



                test.sh: line 7: no: command not found
                ERROR: test.sh:7 no + 5


                instead of (potentially silently) ignoring errors.
                Use -x for debugging;



                bash -x armstrong.sh 222
                ++ echo -n 222
                ++ wc -c
                + P=3
                + SUM=0
                ++ fold -w 1
                ++ echo 222
                + for X in $(echo "$1" | fold -w 1)
                ++ echo '0+(2^3)'
                ++ bc
                + SUM=8
                + for X in $(echo "$1" | fold -w 1)
                ++ echo '8+(2^3)'
                ++ bc
                + SUM=16
                + for X in $(echo "$1" | fold -w 1)
                ++ echo '16+(2^3)'
                ++ bc
                + SUM=24
                + echo 24
                24





                share|improve this answer
























                  up vote
                  0
                  down vote










                  up vote
                  0
                  down vote









                  Use https://www.shellcheck.net (I use it as syntactic vim plugin making a crude IDE)



                  I'd go with this;



                  #!/bin/bash

                  P="$(echo -n "$1" | wc -c)"
                  SUM=0;
                  for X in $(echo "$1" | fold -w 1) ; do
                  SUM=$(echo "$SUM+($X^$P)" | bc );
                  done
                  echo "$SUM"


                  It's not "pure" bash but I find the power of bash is the wide selection of tools, and prioritizing legibility.



                  for stack traces if you add the following to the top of all your scripts it will inform you of errors;



                  set -e
                  trap 'echo "ERROR: $BASH_SOURCE:$LINENO $BASH_COMMAND" >&2' ERR


                  it will stop the script on the error line, make output like



                  test.sh: line 7: no: command not found
                  ERROR: test.sh:7 no + 5


                  instead of (potentially silently) ignoring errors.
                  Use -x for debugging;



                  bash -x armstrong.sh 222
                  ++ echo -n 222
                  ++ wc -c
                  + P=3
                  + SUM=0
                  ++ fold -w 1
                  ++ echo 222
                  + for X in $(echo "$1" | fold -w 1)
                  ++ echo '0+(2^3)'
                  ++ bc
                  + SUM=8
                  + for X in $(echo "$1" | fold -w 1)
                  ++ echo '8+(2^3)'
                  ++ bc
                  + SUM=16
                  + for X in $(echo "$1" | fold -w 1)
                  ++ echo '16+(2^3)'
                  ++ bc
                  + SUM=24
                  + echo 24
                  24





                  share|improve this answer














                  Use https://www.shellcheck.net (I use it as syntactic vim plugin making a crude IDE)



                  I'd go with this;



                  #!/bin/bash

                  P="$(echo -n "$1" | wc -c)"
                  SUM=0;
                  for X in $(echo "$1" | fold -w 1) ; do
                  SUM=$(echo "$SUM+($X^$P)" | bc );
                  done
                  echo "$SUM"


                  It's not "pure" bash but I find the power of bash is the wide selection of tools, and prioritizing legibility.



                  for stack traces if you add the following to the top of all your scripts it will inform you of errors;



                  set -e
                  trap 'echo "ERROR: $BASH_SOURCE:$LINENO $BASH_COMMAND" >&2' ERR


                  it will stop the script on the error line, make output like



                  test.sh: line 7: no: command not found
                  ERROR: test.sh:7 no + 5


                  instead of (potentially silently) ignoring errors.
                  Use -x for debugging;



                  bash -x armstrong.sh 222
                  ++ echo -n 222
                  ++ wc -c
                  + P=3
                  + SUM=0
                  ++ fold -w 1
                  ++ echo 222
                  + for X in $(echo "$1" | fold -w 1)
                  ++ echo '0+(2^3)'
                  ++ bc
                  + SUM=8
                  + for X in $(echo "$1" | fold -w 1)
                  ++ echo '8+(2^3)'
                  ++ bc
                  + SUM=16
                  + for X in $(echo "$1" | fold -w 1)
                  ++ echo '16+(2^3)'
                  ++ bc
                  + SUM=24
                  + echo 24
                  24






                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited Dec 7 at 4:09

























                  answered Dec 7 at 3:55









                  user1133275

                  2,795517




                  2,795517



























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