Variables

fortsh supports shell variables, arrays, associative arrays, and special parameters.

Source: src/scripting/variables.f90

Topics

• Special Variables - $?, $#, $@, etc.
• Arrays - Indexed arrays
• Associative Arrays - Key-value storage
• Environment - Environment variables

Variable Assignment

name=value                    # Simple assignment
name="value with spaces"      # Quoted value
name=$other                   # From another variable
name=$(command)               # From command output
name=$((1 + 2))              # From arithmetic

No spaces around =:

name = value                  # Wrong! Runs "name" with args "=" "value"
name= value                   # Wrong! Sets name to empty, runs "value"
name =value                   # Wrong! Runs "name" with arg "=value"

Using Variables

echo $name                    # Simple expansion
echo ${name}                  # Explicit boundaries
echo "${name}"                # Quoted (preserves whitespace)
echo "Hello, ${name}!"        # Embedded in string

Variable Scope

Global Variables

name="global"
echo $name                    # global

Local Variables (in functions)

myfunc() {
    local name="local"
    echo $name                # local
}
myfunc
echo $name                    # global (unchanged)

Exported Variables

export PATH="$HOME/bin:$PATH"
export EDITOR=vim

# Or in one line
export PATH EDITOR

Exported variables are inherited by child processes.

Variable Attributes

readonly

readonly PI=3.14159
PI=3                          # Error: PI is readonly

export

export VAR=value              # Set and export
export VAR                    # Export existing variable

declare

declare -r CONST=value        # Readonly
declare -x EXPORTED=value     # Exported
declare -i NUMBER=42          # Integer (arithmetic context)
declare -a ARRAY              # Indexed array
declare -A ASSOC              # Associative array

Unsetting Variables

unset name                    # Remove variable
unset -v name                 # Explicitly variable
unset -f func                 # Remove function

Cannot unset readonly variables.

Default Values

${var:-default}               # Use default if unset/empty
${var:=default}               # Set to default if unset/empty
${var:+alternate}             # Use alternate if set/non-empty
${var:?error}                 # Error if unset/empty

See Expansion for full details.

Variable Types

Strings (default)

name="hello world"
echo ${#name}                 # 11 (length)

Integers

declare -i count=0
count=count+1                 # Arithmetic without $(())
echo $count                   # 1

Arrays

arr=(one two three)
echo ${arr[0]}                # one
echo ${arr[@]}                # one two three

Associative Arrays

declare -A map
map[key]=value
echo ${map[key]}              # value

Naming Rules

• Start with letter or underscore
• Contain letters, digits, underscores
• Case-sensitive

valid_name=ok
_also_valid=ok
name2=ok
2name=invalid                 # Cannot start with digit
my-var=invalid                # Hyphens not allowed

Quick Reference