Bash/sh - difference between && and ;
BashShellSyntaxMultiplatformBash Problem Overview
I normally use ; to combine more than one command in a line, but some people prefer &&. Is there any difference? For example, cd ~; cd - and cd ~ && cd - seems to make the same thing. What version is more portable, e.g. will be supported by a bash-subset like Android's shell or so?
Bash Solutions
Solution 1 - Bash
If previous command failed with ; the second one will run.
But with && the second one will not run.
This is a "lazy" logical "AND" operand between operations.
Solution 2 - Bash
I'm using && because a long time ago at the nearby computer:
root# pwd
/
root# cd /tnp/test; rm -rf *
cd: /tnp/test: No such file or directory
...
... and after a while ...
...
^C
but not helped... ;)
cd /tnp/test && rm -rf * is safe... ;)
Solution 3 - Bash
In cmd1 && cmd2, cmd2 is only executed if cmd1 succeeds (returns 0).
In cmd1 ; cmd2, cmd2 is executed in any case.
Both constructs are part of a POSIX-compliant shell.
Solution 4 - Bash
&& means to execute next command if the previous exited with status 0.
For the opposite, use || i.e. to be executed if previous command exits with a status not equal to 0 ; executes always.
Very useful when you need to take a particular action depending on if the previous command finished OK or not.
Solution 5 - Bash
Commands separate by ; are executed sequentially regardless of their completion status.
With &&, the second command is executed only if the first completes successfully (returns exit status of 0).
This is covered in the bash manpage under Lists. I would expect any Unix-like shell to support both of these operators, but I don't know specifically about the Android shell.
Solution 6 - Bash
&& allows for conditional execution while ; always has the second command being executed.
In e.g. command1 && command2, command2 will only execute when command1 has terminated with exit 0, signalling all went well, while in command1 ; command2 the second command will always be executed no matter what the result was of command1.
Solution 7 - Bash
&& is logical AND in bash. Bash has short-circuit evaluation of logical AND. This idiom is a simpler way of expressing the following:
cmd1;rc=$?
if [ $rc -eq 0 ]; then
cmd2
fi
Whereas the ; version is merely:
cmd1
cmd2