Prompting for user input
The following example shows how you can use prompts to explain what the user should enter. michel ~/test> cat friends.sh
#!/bin/bash
# This is a program that keeps your address book up to date.
friends="/var/tmp/michel/friends"
echo "Hello, "$USER". This script will register you in Michel's friends database."
echo -n "Enter your name and press [ENTER]: "
read name
echo -n "Enter your gender and press [ENTER]: "
read -n 1 gender
echo
grep -i "$name" "$friends"
if [ $? == 0 ]; then
echo "You are already registered, quitting."
exit 1
elif [ "$gender" == "m" ]; then
echo "You are added to Michel's friends list."
exit 1
else
echo -n "How old are you? "
read age
if [ $age -lt 25 ]; then
echo -n "Which colour of hair do you have? "
read colour
echo "$name $age $colour" >> "$friends"
echo "You are added to Michel's friends list. Thank you so much!"
else
echo "You are added to Michel's friends list."
exit 1
fi
fi
michel ~/test> cp friends.sh /var/tmp; cd /var/tmp
michel ~/test> touch friends; chmod a+w friends
michel ~/test> friends.sh
Hello, michel. This script will register you in Michel's friends database.
Enter your name and press [ENTER]: michel
Enter your gender and press [ENTER] :m
You are added to Michel's friends list.
michel ~/test> cat friends
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Note that no output is omitted here. The script only stores information about the people Michel is interested in, but it will always say you are added to the list, unless you are already in it.
Other people can now start executing the script: [anny@octarine tmp]$ friends.sh
Hello, anny. This script will register you in Michel's friends database.
Enter your name and press [ENTER]: anny
Enter your gender and press [ENTER] :f
How old are you? 22
Which colour of hair do you have? black
You are added to Michel's friends list.
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After a while, the friends list begins to look like this: tille 24 black
anny 22 black
katya 22 blonde
maria 21 black
--output omitted--
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Of course, this situation is not ideal, since everybody can edit (but not delete) Michel's files. You can solve this problem using special access modes on the script file, see SUID and SGID in the Introduction to Linux guide.
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