checking if a variable is a number

[cwl157]

Is there a way in bash to check if a variable is a number? Like an if statement to check if the variables a number and if it is do one thing if its not do another?

[Franklin52]

You can delete all the numbers of the variable and test if the string is empty.
If

${variable//"[0-9]"}

gives an empty string it is an number.

I suggest you to read some stuff about bash programming, go here for the tutorials:

http://www.tldp.org/LDP/Bash-Beginne...tml/index.html
http://tldp.org/LDP/abs/html/

Regards

[ghostdog74]

simple checking:

echo $var | awk '$0 !~ /[a-zA-Z]/ {print "A number"}'

[drl]

Hi.

Whatever you choose for a specific solution, it will probably involve regular expressions, so you need to decide what "a number" means to you in your problem context. Is it a simple integer? Signed? Decimal fraction? Exponential format? Double precision? Quad precision?

Do you need to diagnose faults, say perhaps with 2 decimal points in a candidate string?

That will determine what characters would be in the regular expression, as well as the complexity.

For example, The AWK Programming Language, has

/^[0-9]+$/

for a pattern in awk that matches a line that consists only of numeric characters. Using grep perhaps in a shell script, you probably would use

'^[0-9]+$'

essentially the same thing except for the shell-isolating-quotes in place of the bounding slashes.

The links from Franklin52 are useful, particularly Chapter 4 of the Beginner link ... cheers, drl