Question

5

"command not found" when using arithmetic expansion in bash shell

rated 0 times [ 5] [ 0] / answers: 1 / hits: 6942 / 1 Year ago, sat, november 26, 2022, 4:02:15

Using Ubuntu Desktop, I have terminal open and I am using the bash shell. One of the shell expansions of bash is the arithmetic expansion, with the following syntax:

$(( EXPRESSION ))

or 

$[ EXPRESSION ]

When i do arithmetic, it does return the correct value but it is always followed by "command not found":

$ $((1+2))

3: command not found

$ $[1+2]

3: command not found

$ $[2+2]

4: command not found

$ $((2*6))

12: command not found

My question is why does it display "command not found" and how can I fix that?

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

kneducator

Add To Favorites

Follow

Total Points: 226

Total Questions: 111

Total Answers: 108

Location: Mexico

Member since Sun, Jul 25, 2021

3 Years ago

answered 1 Year ago eving · Accepted Answer

You have to add echo command before all of your commands,

$ echo $[1+2]

3

You don't have to put directly $[1+2] on terminal, because bash computes $[1+2] and again parses the same, so command not found error occurs.

For Example

$ var="sudo apt-get update"

$ $var



Ign http://archive.canonical.com saucy InRelease                               

Ign http://ppa.launchpad.net saucy InRelease                                   

Ign http://ubuntu.inode.at saucy InRelease                          

Ign http://extras.ubuntu.com saucy InRelease                        

29% [Waiting for headers] [Waiting for headers] [Waiting for headers]

In the above example, sudo apt-get update command was assigned to a variable var.On running $var, first bash expands it and again parses the expanded one.