23

I want to accumulate the line size of a number of files contained in a folder. I have written the following script:

let a=0
let num=0
for i in folder/*
do
        num=`cat $i | wc -l`
        a=$a+$num
done
echo $a

What i am geting at the end of the script is 123+234+432+... and not the result of the arithmetic operation of addition.

47

Your arithmetic evaluation syntax is wrong. Use any of the following (the first is extremely portable but slow, the second is POSIX and portable except to the Bourne shell and earlier versions of the Almquist shell, the last three require ksh, bash or zsh):

a=`expr "$a" + "$num"`

a=$(($a+$num))

((a=a+num))

let a=a+num

((a+=num))

Or you can just skip the entire for loop and just do:

wc -l folder/*

Or, if you only want the total:

cat folder/* | wc -l

Or with zsh and its mult_ios option:

wc -l < folder/*
  • No need for the $ inside ((...)). a=$((a+num)) is already fine. – Weijun Zhou Feb 7 '18 at 8:08
  • if a variable is not set or having null value, would this work, if no any other way to handle that. – Bharat Sep 14 '18 at 13:10
6

you can also use this code

    a=`expr $a + $num`
    echo $a

and MAKE SURE THAT THERE IS A SPACE ON BOTH SIDES OF + IN "$a + $num"

  • always give space on both sides of operator when using expr command for calculation. – user1678213 Nov 7 '12 at 10:45
2

You could declare the type of variable first:

    declare -i a=0
    declare -i num=0
1

Sorry, previous edit was for a different post. Here, just a small modification to the original script:

let a=0
let num=0
for i in folder/*
do
        num=`cat $i | wc -l`
        a=$(echo $a+$num|bc)
done
echo $a
  • 1
    Voted down, as the answer doesn't appear to address the question. – Time4Tea Jan 30 '18 at 22:07
  • Sorry guys, now corrected – Leo Jan 30 '18 at 22:22
0

The answer needs to specify in which shell the code is valid. For instance in the bourne Shell (sh) only the following instructions are valid:

a=$((a+num))
a=$(($a+$num))

while the other possibilities listed by @manatwork may be valid in bourne again shell (bash)

-2

i make it like this

MY_VARIABLE=$((num1+num2))
  • 3
    This adds nothing to what has already been said. – Kusalananda Aug 5 '18 at 14:33
  • it is the brief answer – Hatem Badawi Aug 5 '18 at 16:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.