How to add arithmetic variables in a script

Question

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.

Solution 1

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/*

Solution 2

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"

Solution 3

You could declare the type of variable first:

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

Solution 4

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)

Solution 5

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

View more solutions

Comments

[user1678213]

always give space on both sides of operator when using expr command for calculation.

[Time4Tea]

Voted down, as the answer doesn't appear to address the question.

[Leo]

Sorry guys, now corrected

[Weijun Zhou]

No need for the $ inside ((...)). a=$((a+num)) is already fine.

[Kusalananda]

This adds nothing to what has already been said.

[Hatem Badawi]

it is the brief answer

[Bharat]

if a variable is not set or having null value, would this work, if no any other way to handle that.