Arithmetic on the command line

This is a brief article describing different techniques employed for performing arithmetic operations on the command line.

Using expr:

Using the expr built in is a common way of evaluating arithmetic expressions. Here is an example:

[root@cclient1 ~]# v=10; x=1; expr $v + $x
11

Using let:

Let is another bash built in that can be used for performing arithmetic operations on the command line. Here are a couple of examples:

[root@cclient1 ~]# s=10; let "s+=10"; echo $s
20

 s=10; echo $(($s+10))
20

Both expr & let are easy to use but their drawback is that they can't handle floating point expressions.

For that we have two more commands coming in the picture viz bc & awk.

Using bc:

Invoking bc directly from the command line isn't very useful in a script as we'll usually want the script to be non-interactive. So, here are a few examples of feeding input arithmetic expressions to bc to evaluate:

[root@cclient1 ~]# a=10;b=15; echo "scale=4 ; $a/$b" | bc

.6666

[root@cclient1 ~]#  a=10;b=15; bc <<< "scale=2; $a/$b"

.66

[root@cclient1 ~]# a=100;b=70; echo "$a/$b" | bc -l

1.42857142857142857142

The scale represents the level of precision we want after the floating point. The "-l" options specifies maximum precision possible.

Using awk:

Awk can be used for performing arithmetic operations on it's own as well as on fields extracted from a file.

An example of awk standalone arithmetic usage:

[root@cclient1 ~]# a=10;b=7;  awk "BEGIN {print $a / $b}"

1.42857

If you use the usual ' commas that we're used for enclosing awk expressions then it'll return an error since under ' ' the $ signs get interpreted literally. The BEGIN keyword specifies one time execution.

An example of awk extracting fields from a column & summing the results:

[root@cclient1 ~]# cat file | awk '{ print $1}'

15

8

10

17

26

[root@cclient1 ~]# awk '{ sum += $1} END { print sum}' file

76