Dash

Dash is a shell imperative and scripting language first appearing in 1997.

Hello World

#!/usr/bin/env dash

echo "Hello World!"

Coding Guide

Language Version

dash (Debian Almquist Shell) - POSIX-compliant shell

Execution Model

• Interpreted shell script
• Code executes directly from source
• Scripts run line-by-line from top to bottom
• Uses shebang #!/usr/bin/env dash for execution
• POSIX-compliant shell (minimal, fast)

Key Characteristics

• POSIX-compliant shell (subset of bash features)
• Case-sensitive
• Variables: VAR=value (no spaces around =)
• Command substitution: `command` or $(command)
• String interpolation: "$VAR" or "${VAR}"
• Arithmetic expansion: $((expression))
• Pattern matching: [ string = pattern ] (POSIX [, not bash [[)

Fragment Authoring

Write valid POSIX shell commands. Your fragment becomes the script body. The fragment code will execute as part of the shell script.

Available Commands

Standard Unix utilities and POSIX shell built-ins are available:

• echo - Print text
• printf - Formatted output
• test / [ - Conditional tests (POSIX-compliant)
• if, while, for, until - Control structures
• grep, sed, awk - Text processing (if installed)
• Standard Unix utilities

Common Patterns

• Output: echo "message" or printf "%s\n" "message"
• Variables: NAME="value" and echo "$NAME"
• Conditionals: if [ condition ]; then ... fi
• Loops: for i in 1 2 3 4 5; do echo "$i"; done
• Command substitution: RESULT=$(command)
• Arithmetic: $((A + B))
• Functions: function_name() { ... }
• Here documents: cat <<EOF ... EOF

Examples

# Simple output
echo "Hello from fragment!"

# Variables
NAME="Alice"
echo "Hello, $NAME!"

# Arithmetic
A=5
B=10
SUM=$((A + B))
echo "Sum: $SUM"

# Loops
for i in 1 2 3 4 5; do
    echo "Count: $i"
done

# Conditionals
if [ "$1" = "test" ]; then
    echo "Testing mode"
else
    echo "Normal mode"
fi

# Functions
greet() {
    local name="$1"
    echo "Hello, $name!"
}

greet "World"

# Command substitution
DATE=$(date)
echo "Current date: $DATE"

# Multiple statements
echo "First line"
echo "Second line"
echo "Third line"

# Arithmetic in loops
for i in $(seq 1 5); do
    echo "Number: $i"
done

# Nested conditionals
if [ -n "$1" ]; then
    if [ "$1" = "hello" ]; then
        echo "Greeting received"
    else
        echo "Other argument: $1"
    fi
else
    echo "No argument provided"
fi

Caveats

• Variable assignment: no spaces around =
• Use [ for tests (POSIX-compliant), not [[ (bash-specific)
• String comparison: use = not == in [ tests
• Quote variables to prevent word splitting: "$VAR"
• No bash-style arrays (use space-separated strings or $IFS)
• No brace expansion like {1..5} (use seq or explicit lists)
• Arithmetic expansion: $((expression)) (no $ inside)
• Function definitions: function_name() { ... } (POSIX style)
• Use local keyword inside functions to avoid global variable pollution
• Dash is minimal - avoid bash-specific features

Fraglet Scripts

Dash Fortune

#!/usr/bin/env -S fragletc --vein=dash
# One from the vault: dash fortunes
echo "Dash: because 100KB is a feature."

Echo Args

#!/usr/bin/env -S fragletc --vein=dash
echo "Args: $*"

Stdin Upper

#!/usr/bin/env -S fragletc --vein=dash
while read -r line; do echo "$line" | tr "a-z" "A-Z"; done

Test

#!/usr/bin/env -S fragletc --vein=dash

echo "Hello World!"

Connections

Container Info