I used to believe that the appropriate way of breaking the lines in a list is
command1 && \
command2
It turned out that it isn't so , one doesn't need \
$ [ $(id -u) -eq 1000 ] &&
> echo yes
yes
The same works with pipes | the same way.
The bash man page sections on pipelining and lists didn't shed any light on this. Thus , my question is : what is the proper usage of \ to break long lines ?
If the statement would be correct without continuation, you need to use \. Therefore, the following works without a backslash, as you can't end a command with a &&:
echo 1 &&
echo 2
Here, you need the backslash:
echo 1 2 3 \
4
or
echo 1 \
&& echo 2
Otherwise, bash would execute the command right after processing the first line without waiting for the next one.
&& and it gives PS2 prompt. What are some of the other cases ? Is there a list somewhere in the bash manual?
One of the scripting style guidelines I've encountered during my professional life at a huge IT company, obligated me to use no longer than 80 characters per line in a shellscript and indenting after breaking the line. Also, I had to break line before a pipe or && or ||. Like :
command1 \
&& command2 \
|| command3 \
| command4
The goal was to have a clear readability.
&& and || at the beginning of lines. Just like I put the OR and AND at the beginning of lines in my SQL WHERE clauses.
` and in other cases it is optional, I would prefer to use ` everywhere that my command continues on the next line. Scanning a script you can easily miss that a line is continued because it ends with && or || or |. (And as @ErikE says, i actually prefer to have my && and || on the next line).