Which one is better: using ; or && to execute multiple commands in one line?

In tutorials and how-to's I often see commands combined. For instance,

sudo apt-get update && sudo apt-get install pyrenamer

There seem to be four possible connectors: &, &&, || and ;. Though the & connector is clear to me (it sends a process to the background and leaves the terminal available), it is not clear what the difference is between && and ;. And I did not know of || until Kaya's comment.

The following questions deal with the difference between the two connectors, but do so mostly in the comments:

• How to start two Ubuntu applications in one go?

• How to combine multiple commands in terminal?

So here are a number of related questions:

1. What is the difference between ; and &&?
2. When should you use them respectively? It would be nice to see some use cases: if I want to run a command and then after it shutdown my computer, which connector should I choose?
3. What are their advantages and dangers? Robie Basak mentions in a comment to this answer that a command like cd /somewhere_else; rm -Rf * can have destructive consequences if the first element in the command chain fails, for instance.
4. If relevant, where do they come from?

Solution 1:

Cheatsheet:

A; B    # Run A and then B, regardless of success of A
A && B  # Run B if and only if A succeeded
A || B  # Run B if and only if A failed
A &     # Run A in background.

Solution 2:

&& only runs the second command if the first one exited with status 0 (was successful). ; runs both the commands, even if the first one exits with a non zero status.

Your example with && can be equivalently paraphrased as

if sudo apt-get update ; then
    sudo apt-get install pyrenamer
fi

Solution 3:

Using ; will execute the commands irrespective whether first command is successful or not.

Using && will execute the second command only when first command executed successfully (status 0).

Both are used on different perspective. Like for a longer process, say for an installation you need to compile and install it. you should make && make install. So the install will run only if make successful.

So for dependent commands you should use &&.

Wring bash, or commands with independent commands, use ;.

So if you want to shutdown computer even the first job failed use ; , but if want on complete success of first job initiate the shutdown use &&.

Solution 4:

a ; b will run b regardless of the exit status of a. a && b will run b only if a succeeded.

This is necessary and sufficient to answer to the first 3 questions. In particular, the 2 is too broad, and cannot be given "one" definitive answer - your best bet is to decide on a case by case basis.

As for the 4th question: They're Bash syntax.

There is no intrinsic danger in using either. Again, the definition above is sufficient. It implies that you will write && when b has unintended effects if a does not succeed. There is no need for further rules or explanation, IMHO.