Bash: Testing if a variable is an integer

Question

Hello,

I have a bash scripting question please.

I would like to test if my variable $var is actually an integer or not.

How can I please do that?

Thank you very much,

Jary

Answer 1

echo your_variable_here | grep "^-\?[0-9]*$" will return the variable if it is an integer and return nothing otherwise.

Answer 2

BASH FAQ entry #54

Answer 3

shopt -s extglob
case "$var" in
 +([0-9]) ) echo "integer";
esac

Answer 4

function is_int() { return $(test "$@" -eq "$@" > /dev/null 2>&1); }

input=0.3
input="a b c"
input=" 3 "
if $(is_int "${input}");
   then
   echo "Integer: $[${input}]"
else
   echo "Not an integer: ${input}"
fi

Answer 5

I was needing something that would return true only for positive integers (and fail for the empty string). I settled on this:

test -n "$1" -a "$1" -ge 0 2>/dev/null

the 2>/dev/null is there because test prints an error (and returns 2) if an input (to -ge) doesn't parse as an integer

I wish it could be shorter, but "test" doesn't seem to have a "quiet" option and treats "" as a valid integer (zero).