Shell Programming and Scripting

#!/bin/bash
# name: loginname_validate
# purpose: to validate the loginname which is used to add a new user
i=0
while [ $i -ne 1 ]
do
	read -p "Please enter a new loginname: " loginname
	if [ -z "$loginname" ]
	then
		echo "You should enter a nonempty loginname."
		continue 1
	elif [ ${#loginname} -lt 8 -o ${#loginname} -gt 16 ]
	then
		echo "The length of loginname must between 8 and 16 characters long."
		continue 1
	elif echo "$loginname" | awk '/^[-a-Z]/ && /[a-z]/ && /[A-Z]/ && /[0-9]/ && /\W/ { X=1 } END { exit(!X) }'
	then
		echo "You have entered a valid loginname."
		break
	else
		echo "The loginname, which you entered, must start with a underscore or an alphabet, and it must contain at least one lowercase and one uppercase and one digit and one punctuation."
		continue 1
	fi
done

# Create a variable i
typeset i=value

# Does i meet condition 1
if [ i == whatever condition 1 ]
then
        # Does i meet condition 2
        if [ i == whatever condition 2 ]
        then
                # Does i meet condition 3
                if [ i == whatever condition 3 ]
                then
                        # Action if all conditions are met
                else
                        # Action if i does not meet condition 3
                fi
        else
                 # Action if i does not meet condition 2
        fi
else
        # Action if i does not meet condition 1
fi

# Create a variable i
typeset i=value

until typeset i=J; [ "$i" cond1 -a "$i" cond2 -a "$i" cond3 ]; do :; done