Anything that has been extended with Bash, etc.,nois the data type for shell scripts considered within the scope of#!/bin/sh. Everything is a string.

expris in command format, but what you receive is anumber string, not the number itself.

Check whether the given data is a numerical value with a regular expression, or check if it can be calculated by throwing toexprorbc, etc. There is a way.

If you want to check integers, strings, and arrays using thedeclareandtypesetcommands in Bash, use-poption of the>declarecommand.

# Declaring variable i as an integer
declare -i i = 1
# increment i and display
i = i + 1
echo $i # =>2
# check how it was declared with declare -p
declare -p i
# declare -i i
# Is displayed, so use this

In zsh, you can check the variable type as${(t) foo}.

declare -i i = 1
echo ${(t) i}
# integer
# Is displayed
s = hoge
echo ${(t) s}
# scalar
# Is displayed

If you want to be POSIX compliant, there's no type of variable in the first place. If you want to check if the contents of a variable are something like an integer, usegrepetc.

i = 0
if echo "$i" | head -n1 | grep '^ [0-9] \ + $'>/dev/null;then
  echo "integer"
else
  echo "not integer"
fi

is good.

See theman bashtypesetdeclaresection of the built-in command for the attributes of the variable.

Do you want to judge whether it's a string consisting only of numbers or a string that contains other than numbers?

if test -n "$A" -a -z "${A // [0-9] /}"
then echo only numbers
else echo Non-numeric or empty
fi

(If you delete all the numbers and are empty, say that the original string was only numbers.)