CODEWITHSUNDEEP
bashshell
hollabaloo
hollabaloo

Reputation: 853

Linux Regular Expression

I'm working with shell scripting in Linux. I want to check if the value of MAX_ARCHIVE_AGE is numeric or not. My code is like this:

MAX_ARCHIVE_AGE = "50"

expr="*[0-9]*"

if test -z "$MAX_ARCHIVE_AGE";
then
    echo "MAX_ARCHIVE_AGE variable is missing or not initiated"
else
    if [ "$MAX_ARCHIVE_AGE" != $expr ]
    then
        echo "$MAX_ARCHIVE_AGE is not a valid value"
    fi
fi

I want to match the value of MAX_ARCHIVE_AGE with my expr. Please help.

Upvotes: 1

Views: 124

Answers (2)

tripleee
tripleee

Reputation: 189327

For POSIX compatibility, look at case. I also find it more elegant than the corresponding if construct, but the syntax may seem a bit odd when you first see it.

case $MAX_ARCHIVE_AGE in
  '' ) echo "empty" >&2 ;;
  *[!0-9]* ) echo "not a number" >&2 ;;
esac

By the way, notice the redirection of error messages to standard error with >&2.

Upvotes: 4

ruakh
ruakh

Reputation: 183251

Your expr will match anything that contains any digits; it's better to check if it contains only digits, or conversely, to check if it contains any non-digits. To do that, you can write:

if ! [[ "$MAX_ARCHIVE_AGE" ]] ; then
    echo "MAX_ARCHIVE_AGE is blank or uninitialized" >&2
elif [[ "$MAX_ARCHIVE_AGE" == *[^0-9]* ]] ; then
    echo "$MAX_ARCHIVE_AGE is not a valid value" >&2
fi

Also, note that you would initialize MAX_ARCHIVE_AGE by writing e.g. MAX_ARCHIVE_AGE=50 (no spaces), not MAX_ARCHIVE_AGE = 50. The latter tries to run a program called MAX_ARCHIVE_AGE with the arguments = and 50.

Upvotes: 2

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