Check if string equals asterisk in Bash scripting?

Question

I'm making a bash script to do basic arthmetic and when I do:

if [ $2 == "*" ]

it does not work.

How can I check for asterisk?

Solution 1

You need to escape or quote the asterisk in the command line:

./calculator.sh 2 \* 2
./calculator.sh 2 '*' 2

and enclose the $2 in double quotes:

if [ "$2" == "*" ]

Solution 2

The problem isn't that the if statement isn't working, it is that the asterisk on the command line is being globbed.

So if your script was called mycalc and run from the command line you do

mycalc 2 * 3

The * will get globbed, and converted to all the names of the files in the current folder.

To avoid expansion, you would need to do

mycalc 2 \* 3

The \ escapes the asterisk and passes it through without changing it.

You might want to consider x for the multiplication operation to avoid this.

Comments

[JdeBP]

Unix Philosophy 102: Let the shell do what the shell does best, and use bc or dc if you want a calculator.

[Ignacio Vazquez-Abrams]

Oh good. For a moment I thought I'd need to beat someone over the head with the BASH FAQ.

[pabouk - Ukraine stay strong]

Unfortunately you do not say how to use the ASCII value for the condition checking.