While both ; and && allow executing multiple commands on a single line, they handle command execution flow fundamentally differently:

# Semicolon example (unconditional execution)
command1 ; command2

# Double ampersand example (conditional execution)
command1 && command2

The critical difference lies in how they handle exit statuses:

false ; echo "This will run"  # Executes regardless of first command's success
false && echo "This won't run" # Only executes if first command succeeds

Semicolon use case: When you need sequential execution regardless of success

make clean ; make  # Always try to build even if clean fails

Double ampersand use case: When execution should halt on failure

./configure && make && make install  # Classic build chain

The && operator can save execution time by failing fast:

# Stops at first failing test
test_connection && download_file && process_data

Combine both operators for sophisticated control flows:

# Attempt primary method, fallback to secondary on failure
primary_command || { fallback_command ; cleanup }

Always prefer && for critical operations where failure should stop execution:

[[ -d "/valid/path" ]] && cd "/valid/path" || exit 1

Use ; for unrelated operations or when you explicitly want to continue after failures:

rm old_file.log ; touch new_file.log

Here's a real-world deployment script example:

# Stop deployment if any step fails
npm ci && \
npm run build && \
rsync -avz dist/ deploy@server:/app && \
ssh deploy@server "sudo systemctl restart myapp"

While both the semicolon (;) and double ampersand (&&) can execute multiple commands in one line, their underlying logic differs significantly:

# Semicolon example (unconditional execution)
command1 ; command2

# Double ampersand example (conditional execution)
command1 && command2

The semicolon acts as a simple command separator, while && implements logical AND behavior:

# Will attempt ls even if cd fails
cd /nonexistent ; ls -al

# Will abort if cd fails
cd /nonexistent && ls -al

The critical difference lies in exit status handling:

false ; echo "This always runs"  # Exit status 0
false && echo "Never reaches here"  # Exit status 1

For &&:

make && sudo make install  # Only install if build succeeds

For ;:

cleanup ; reboot  # Force both operations regardless

Chaining with && can save execution time by early termination:

# Stops at first failing test
test1 && test2 && test3 && deploy

Advanced scripts often combine both for complex logic:

precheck && (setup ; configure) || error_handling