How to add in shell script?

Question

Assume let the value of the variable a be 42,

b=18+$a
The value of b should be 60

But I'm not getting the value 60. Instead it's printing 18+42. How can i do it ?

New Query :

grep -F "$name" -A1000 filename | sed -n '1p;19p;24p'

Assume let a=10,b=20,c=30.In the above grep command can i use '$ap;$bp;$cp' instead of '1p;19p;24p' ?

Another thing, I've given as -A1000. Which implies that starting from 1p it considers till 1000 line , right ? I need to search throughout file without giving the number. Ho

Community · Accepted Answer · 2020-06-20 09:12:55Z

6

Bash:

b=$((18+a))
echo "value of b is $b"

or

let b=18+a
echo "value of b is $b"

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jun 5, 2012 at 10:25

Prince John Wesley

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11 Comments

Jackie James Over a year ago

@ Prince : Thank U. By the way do u remember this grep -F "$name" -A37 filename| sed -n '1p;19p;24p' ;which u've guided me yesterday ? In the above command can i mention '$ap;$bp;$cp' instead of '1p;19p;24p' ?

sorpigal Over a year ago

Inside $(()) and on the right side of a let statement the use of the dollar sign is not required. E.g. let b=18+a would work just as well.

sorpigal Over a year ago

@JackieJames: Variables don't expand inside single-quoted strings. In addition, bash would not see "A variable named a followed by the letter p," for example, instead i would see "A variable named ap," which is not what you mean. You should double-quote the expansion and include curly braces for clarity: "${a}p;${b}p;${c}p"

Jackie James Over a year ago

@ Prince : grep -F "$name" -A1000 filename | sed -n '1p;19p;24p' Assume let a=10,b=20,c=30.In the above grep command can i use '$ap;$bp;$cp' instead of '1p;19p;24p' ? Another thing, I've given as -A1000. Which implies that starting from 1p it considers till 1000 line , right ? I need to search throughout file without giving the number.

Prince John Wesley Over a year ago

@JackieJames: use double quotes

|

rajatkhanduja · Accepted Answer · 2012-06-05 10:33:52Z

1

Any mathematical operation in Bash involves the use of $(())

So, for addition, you would do :-

b=$((18 + a))

Notice that the '$' before a is not required. Some more examples of mathematical operations in Bash are :-

a=$((17+1))
b=$((100-a))
c=$((a*b))
d=$((c/b))
echo $((10 * 1024 * 1024)) # Echoes the number bytes in 10 MB

answered Jun 5, 2012 at 10:33

rajatkhanduja

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