🔧 Variables

Variables let you store and reuse information. This guide covers how to create variables, use their values, and check if they exist.

---

Defining Variables

To create a variable, use the = symbol with no spaces around it. Here's the basic syntax:

VARIABLE_NAME="VALUE"

note

• Variable names are case-sensitive ("a" and "A" are distinct).
• Names must start with an alphabetic character or "_" (e.g., "A", "__A"). Starting with numbers (e.g., "90", "90__MyVar") is invalid.
• After the first character, names can include letters, numbers, or "_" (e.g., "MyVar__90").

warning

Avoid using variable names starting with ___ (three underscores). This prefix is reserved for provisional environment variables used internally by DI. Using it in your scripts may cause conflicts or data loss.

Examples

a="Ole"
A="Just test"
A10="a b c d e"
_A="1 2 3 4 5"
B_="W e l c o m e !"
B_1_2_3="-------------------------"

tip

Always enclose the value in quotes (") to handle spaces or special characters safely.

---

Using Variables

To use a variable’s value, add a $ before its name. This tells the script to replace $VARIABLE_NAME with its stored value.

Basic Usage

greeting="Hello"
ui_print "$greeting everyone"  # Prints "Hello everyone"

Avoiding Confusion with Braces

If a variable is followed by text that could mix with its name, use ${} to clearly separate it:

name="Alice"
ui_print "$name123"       # Tries to use "name123", not only "name"
ui_print "${name}123"     # Prints "Alice123"

---

Checking If Variables Are Defined

Sometimes you need to know if a variable has been created. Use defined to check if it exists, or undefined to check if it doesn’t.

defined

Checks if one or more variables are set.

Argument	Description
VAR	Variable(s) to check (multiple allowed)

name="Alice"
if defined name; then
    ui_print "Name is set"
fi

# Multiple variables
age="25"
if defined name age; then
    ui_print "Both name and age are set"
fi

undefined

Checks if one or more variables are not set.

Argument	Description
VAR	Variable(s) to check (multiple allowed)

if undefined score; then
    ui_print "Score is not set"
fi

# Multiple variables
if undefined score level; then
    ui_print "Score and level are not set"
fi

Practical Example

user="Bob"
if defined user; then
    ui_print "User is $user"
else
    ui_print "No user defined"
fi

if undefined points; then
    points="0"  # Set a default value
    ui_print "Points set to $points"
fi