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Overview

The true and false commands are utility commands that do nothing except return a specific exit status. true always succeeds (exit code 0), and false always fails (exit code 1). They are primarily used in conditional logic, loops, and testing.

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Syntax

true
false

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Description

The true command:
  • Performs no operation
  • Always returns exit code 0 (success)
  • Produces no output
  • Accepts no arguments (arguments are ignored)

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Exit Status

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true
command
Always returns 0 (success)
true
echo $?
# Output: 0
​
false
command
Always returns 1 (failure)
false
echo $?
# Output: 1

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Examples

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Basic Usage

true
echo $?
# Output: 0

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With && Operator

# Second command runs because first succeeds
true && echo "This runs"
# Output: This runs

# Second command doesn't run because first fails
false && echo "This won't run"
# Output: (nothing)

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With || Operator

# Second command doesn't run because first succeeds
true || echo "This won't run"
# Output: (nothing)

# Second command runs because first fails
false || echo "This runs"
# Output: This runs

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In Conditional Statements

if true; then
  echo "Always executes"
fi
# Output: Always executes

if false; then
  echo "Never executes"
else
  echo "Always executes"
fi
# Output: Always executes

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Practical Use Cases

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Infinite Loops

# Loop forever (until break or Ctrl-C)
while true; do
  echo "Processing..."
  # do work
  # break condition
done

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Default Success/Failure

# Ensure script succeeds even if last command fails
some_command || true

# Ensure script fails for testing
some_test_setup
false  # Force failure for testing

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Placeholder Commands

# Temporarily disable a command during development
# some_long_command --with-options
true  # Placeholder while debugging

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Logic Testing

# Test conditional logic
if false || true; then
  echo "OR logic works"
fi
# Output: OR logic works

if true && false; then
  echo "Won't run"
else
  echo "AND logic works"
fi
# Output: AND logic works

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Safe Command Chains

# Continue even if optional command fails
optional_command || true
required_command  # This still runs

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No-op in Scripts

# Syntactic placeholder (like 'pass' in Python)
if test -f config.json; then
  true  # TODO: implement config loading
else
  echo "Using defaults"
fi

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Testing Exit Status Handling

# Test error handling code
if false; then
  echo "This won't run"
else
  echo "Error handling works"
fi
# Output: Error handling works

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Advanced Examples

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Loop Control

# Infinite loop with break condition
COUNTER=0
while true; do
  echo "Count: $COUNTER"
  COUNTER=$((COUNTER + 1))
  test "$COUNTER" -ge 5 && break
done
# Output:
# Count: 0
# Count: 1
# Count: 2
# Count: 3
# Count: 4

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Conditional Assignment

# Set variable based on condition
SUCCESS=false
some_command && SUCCESS=true

if $SUCCESS; then
  echo "Command succeeded"
fi

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Default Behavior

# Provide fallback behavior
complex_command || true
echo "Script continues regardless"

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Circuit Breaker Pattern

# Stop on first failure
step1 || false
step2 || false
step3 || false
echo "All steps succeeded"

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Negation

# Logical NOT using !
true && echo "true is true"
# Output: true is true

false || echo "false is false"
# Output: false is false

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Comparison with test Command

Fixed exit codes:
true   # Always 0
false  # Always 1

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Common Patterns

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Continue on Error

# Ignore errors from optional cleanup
rm temp.txt || true

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Ensure Loop Iteration

# Infinite service loop
while true; do
  echo "Service running..."
  # service work
  sleep 1
done

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Stub Functions

# Placeholder for future implementation
my_function() {
  true  # TODO: implement this
}

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Force Exit Code

# Ensure script exits with specific code
some_complex_script
true   # Always exit with 0
# OR
some_complex_script
false  # Always exit with 1

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Short-circuit Evaluation

# Only run if all conditions met
true && true && true && echo "All true"
# Output: All true

# Run if any condition met
false || false || true || echo "Never reached"
# Output: (nothing - short-circuited at true)

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Boolean Logic Examples

# AND truth table
true && true && echo "T && T = T"      # Runs
true && false && echo "T && F = F"     # Doesn't run
false && true && echo "F && T = F"     # Doesn't run
false && false && echo "F && F = F"    # Doesn't run

# OR truth table
true || true && echo "T || T = T"      # Runs
true || false && echo "T || F = T"     # Runs
false || true && echo "F || T = T"     # Runs
false || false || echo "F || F = F"    # Runs (demonstrates F || F = F with echo)

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While Loop Patterns

while true; do
  # runs forever
done

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Notes

  • Both commands accept any arguments but ignore them completely
  • No output is ever produced (stdout and stderr remain empty)
  • Useful for logic testing and script control flow
  • Common in shell scripting for loops and conditionals
  • Exit codes are guaranteed: true = 0, false = 1
  • Can be used as no-op (no operation) placeholders
Infinite loops with while true will run forever unless:
  • A break statement is executed
  • The script is killed (Ctrl-C)
  • An error occurs with -e shell option set
  • An exit command is called
# This will run forever!
while true; do
  echo "Infinite loop"
done
# Press Ctrl-C to stop
  • test - Evaluate conditional expressions
  • which - Check command availability

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