How can I add numbers in a Bash script

Question

I have this Bash script and I had a problem in line 16  How can I take the previous result of line 15 and add it to the variable in line 16      bin bash  num 0 metab 0  for   i 1  i lt  2  i      do     for j in  ls output- i-    do         echo   j           metab   cat  j grep EndBuffer awk   sum   2  END   print sum 120     line15          num   num    metab    line16      done     echo   num   done

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use a shell built-in let   it is similar to    expr     A 1 B 1 let  C    A    B  echo  C   C    2   source  https   www computerhope com unix bash let htm

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There are a thousand and one ways to do it  Here s one using dc  a reverse-polish desk calculator which supports unlimited precision arithmetic    dc  lt  lt  lt   num1  num2   p    But if that s too bash-y for you  or portability matters  you could say  echo  num1  num2   p   dc   But maybe you re one of those people who thinks RPN is icky and weird  don t worry  bc is here for you   bc  lt  lt  lt    num1    num2  echo  num1    num2   bc   That said  there are some unrelated improvements you could be making to your script      bin bash  num 0 metab 0  for   i 1  i lt  2  i      do     for j in output- i-    do    for  can glob directly  no need to ls             echo   j                   grep  can read files  no need to use  cat              metab   grep EndBuffer   j    awk   sum   2  END   print sum 120                num      num    metab        done     echo   num  done   As described in Bash FAQ 022  Bash does not natively support floating point numbers  If you need to sum floating point numbers the use of an external tool  like bc or dc  is required   In this case the solution would be  num   dc  lt  lt  lt   num  metab   p     To add accumulate possibly-floating-point numbers into num

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bin bash  num 0 metab 0  for   i 1  i lt  2  i      do           for j in  ls output- i-    do         echo   j           metab   cat  j grep EndBuffer awk   sum   2  END   print sum 120     line15          let num num metab  line 16      done     echo   num  done

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In bash    num 5  x 6     num    x     echo  num        gt  11   Note that bash can only handle integer arithmetic  so if your awk command returns a fraction  then you ll want to redesign  here s your code rewritten a bit to do all math in awk   num 0 for   i 1  i lt  2  i      do           for j in output- i-   do         echo   j          num               awk -v n   num                    EndBuffer   sum     2                 END  print n    sum 120                  j                done     echo   num  done

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bin bash read X read Y echo      X  Y

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Use the        arithmetic expansion   num      num    metab      See Chapter 13  Arithmetic Expansion for more information

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I always forget the syntax so I come to google  but then I never find the one I m familiar with  P  This is the cleanest to me and more true to what I d expect in other languages   i 0   i      echo  i

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For integers    Use arithmetic expansion     EXPR    num    num1   num2   num     num1    num2           Also works num    num1   2   3                num   num1 num2                Old  deprecated arithmetic expression syntax  Using the external expr utility  Note that this is only needed for really old systems   num  expr  num1    num2        Whitespace for expr is important      For floating point   Bash doesn t directly support this  but there are a couple of external tools you can use   num   awk  BEGIN  print  num1  num2  exit    num   python -c  print  num1  num2   num   perl -e  print  num1  num2   num   echo  num1    num2   bc      Whitespace for echo is important   You can also use scientific notation  for example  2 5e 2      Common pitfalls    When setting a variable  you cannot have whitespace on either side of    otherwise it will force the shell to interpret the first word as the name of the application to run  for example  num  or num   num  1 num  2 bc and expr expect each number and operator as a separate argument  so whitespace is important  They cannot process arguments like 3   4   num  expr  num1   num2

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You should declare metab as integer and then use arithmetic evaluation  declare -i metab num     num  metab       For more information see https   www gnu org software bash manual html node Shell-Arithmetic html Shell-Arithmetic

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Another portable POSIX compliant way to do in bash  which can be defined as a function in  bashrc for all the arithmetic operators of convenience   addNumbers          local IFS         printf   s n                  and just call it in command-line as   addNumbers 1 2 3 4 5 100 115   The idea is to use the Input-Field-Separator IFS   a special variable in bash used for word splitting after expansion and to split lines into words  The function changes the value locally to use word-splitting character as the sum operator     Remember the IFS is changed locally and does NOT take effect on the default IFS behaviour outside the function scope  An excerpt from the man bash page      The shell treats each character of IFS as a delimiter  and splits the results of the other expansions into words on these characters  If IFS is unset  or its value is exactly   the default  then sequences of     and  at the beginning and end of the results of the previous expansions are ignored  and any sequence of IFS characters not at the beginning or end serves to delimit words     The             represents the list of arguments passed to be split by   and later the sum value is output using the printf function  The function can be extended to add scope for other arithmetic operations also

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I really like this method as well  less clutter   count   count 1

[bash] How can I add numbers in a Bash script?

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