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I just can't figure out how do I make sure an argument passed to my script is a number or not.
All I want to do is something like this:
test *isnumber* $1 && VAR=$1 || echo "need a number" Any help?
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One way is to check whether it contains non-number characters. You replace all digit characters with nothing and check for length -- if there's length there's non-digit characters. If input is 5b for example, it will fail check.
To check if a variable is set in Bash Scripting, use-v var or-z ${var} as an expression with if command. This checking of whether a variable is already set or not, is helpful when you have multiple script files, and the functionality of a script file depends on the variables set in the previously run scripts, etc.
One approach is to use a regular expression, like so:
re='^[0-9]+$' if ! [[ $yournumber =~ $re ]] ; then echo "error: Not a number" >&2; exit 1 fi If the value is not necessarily an integer, consider amending the regex appropriately; for instance:
^[0-9]+([.][0-9]+)?$ ...or, to handle numbers with a sign:
^[+-]?[0-9]+([.][0-9]+)?$ Without bashisms (works even in the System V sh),
case $string in ''|*[!0-9]*) echo bad ;; *) echo good ;; esac This rejects empty strings and strings containing non-digits, accepting everything else.
Negative or floating-point numbers need some additional work. An idea is to exclude - / . in the first "bad" pattern and add more "bad" patterns containing the inappropriate uses of them (?*-* / *.*.*)
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