Re: if (()){}else{} documented?

[zzapper <zsh@rayninfo.co.uk>]

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On 20/04/2021 16:33, Lawrence Velázquez wrote:
> SIMPLE COMMANDS & PIPELINES

A /sublist/ is either a single pipeline, or a sequence of two or more 
pipelines separated by ‘&&’ or ‘||’. If two pipelines are separated by 
‘&&’, the second pipeline is executed only if the first succeeds 
(returns a zero status). If two pipelines are separated by ‘||’, the 
second is executed only if the first fails (returns a nonzero status). 
Both operators have equal precedence and are left associative. The value 
of the sublist is the value of the last pipeline executed. For example,

dmesg | grep panic && print yes

is a sublist consisting of two pipelines, the second just a simple 
command which will be executed if and only if the grep command returns a 
zero status. If it does not, the value of the sublist is that return 
status, else it is the status returned by the print (almost certainly 
zero).

A /list/ is a sequence of zero or more sublists, in which each sublist 
is terminated by ‘;’, ‘&’, ‘&|’, ‘&!’, or a newline. This terminator may 
optionally be omitted from the last sublist in the list when the list 
appears as a complex command inside ‘(...)’ or ‘{...}’. When a sublist 
is terminated by ‘;’ or newline, the shell waits for it to finish before 
executing the next sublist. If a sublist is terminated by a ‘&’, ‘&|’, 
or ‘&!’, the shell executes the last pipeline in it in the background, 
and does not wait for it to finish (note the difference from other 
shells which execute the whole sublist in the background). A 
backgrounded pipeline returns a status of zero.

More generally, a list can be seen as a set of any shell commands 
whatsoever, including the complex commands below; this is implied 
wherever the word ‘list’ appears in later descriptions. For example, the 
commands in a shell function form a special sort of list.


lv thanks will digest


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