I'm writing a small script thats purpose is to validate a single command line argument to make sure it is an integer. Also acceptable are a leading "+" or "-", but no more than one.

Example: "5" "-2" "+4" are all valid

If its invalid I simply print out a message saying so, otherwise I just return the value (I need to remove the leading "+" though).

Here's the code I have so far:

# Checks for valid number of arguments
# Exits program with return code of 1
if [ $# -ne 1 ]; then
        echo "Invalid number of arguments; supports only one argument"

        exit 1
fi

# Checks for valid argument
echo $1 | egrep -s "^[+|-]?[0-9]+$"

# If argument is valid then return its value
# Exits program with return code of 0
if [ $? -eq 0 ]; then
        # Removes a leading '+' sign if there is one
        tr -d '+' $1
        echo $1

        exit 0
# If argument is invalid then return an error message
# Exits program with return code of 2
else
        echo "Invalid operand: $1"

        exit 2
fi