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regexlinuxshellnumbersash

How to test if variable is a number with certain max digits in linux non-bash shell script

Here I found nice solution to test if variable is a number:

case $string in
   ''|*[!0-9]*) echo bad ;;
   *) echo good ;;
esac

I'm trying to modify it to test if variable is a 1,2,3 or 4-digit natural number (within a range 0-9999), so I added |*[0-9]{5,}* to exclude numbers with more than 5 digits, but the code below prints good for numbers greater then 9999 e.g. 1234567.

case $string in
   ''|*[!0-9]*|*[0-9]{5,}*) echo bad ;;
   *) echo good ;;
esac

I'm using ash from busybox.

Solution

  • Not sure if you need this in a case statement, since I would just do:

    if { test "$string" -ge 0 && test "$string" -lt 10000; } 2> /dev/null; then
  echo good
else 
  echo bad
fi

    If you want to use a case statement in a strictly portable shell, you're probably stuck with:

    case $string in 
    [0-9]|[0-9][0-9]|[0-9][0-9][0-9]|[0-9][0-9][0-9][0-9]) echo good;;
     *) echo bad;;
esac