Question: I have a requirement to add 10 days to current date and assign it to a variable. But I am getting error:

```
date: illegal option -- d

```

This is what I tried:

```
$> NEW_expration_DATE=$(date -d "+10 days")

```

Result:

```
date: illegal option -- d
Usage: date [-u] [+Field Descriptors]

```

Answer: 
Try this: 
NEW\_expration\_DATE=$(gdate -d "+10 days")
It looks like you are using a **POSIX shell**, and that there is **no way** to do simple date arithmetic in here. 

I found a guy who explains it and who coded something to substract dates. You may be able to adapt it for your case: <https://unix.stackexchange.com/a/7220/162444>

Good luck!