Comparing numbers in various forms from a shell script

Question

I'm going to be retrieving two numbers as strings into variables A and B:

A will be in the form:

"10" or "0x0A" or "0x0a"

In other words, A will be either a decimal or hexadecimal number (with 0x prefix).

B will be in the form:

"image-000A" or "image-000a"

B will always be "image-" followed by 4 hexadecimal digits.

I need to compare the two numeric values and test if B > A. How do I do that in a shell script?

rojo · Accepted Answer · 2013-02-20 18:57:35Z

2

You can convert a hex number to decimal simply by multiplying it by 1.

rojo@pico:~$ t=0x0a
rojo@pico:~$ echo $t
0x0a
rojo@pico:~$ echo $(( $t * 1 ))
10

Scraping the hex value from the image is slightly more complicated, but still works the same way.

rojo@pico:~$ t=image-000a
rojo@pico:~$ echo $t
image-000a
rojo@pico:~$ echo $(( 0x${t##image-} * 1 ))
10

The ${t##image-} strips image- out of $t, leaving 000a.

answered Feb 20, 2013 at 18:42

rojo

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