1 Eylül 2021 Çarşamba tarihinde Robert Elz <k...@munnari.oz.au> yazdı:
> Date: Wed, 1 Sep 2021 16:38:00 +0300 > From: "=?UTF-8?B?T8SfdXo=?= via austin-group-l at The Open > Group" <austin-group-l@opengroup.org> > Message-ID: <CAH7i3LpFk0TfxwpQny3ma6HzMptS > qvsysq5nfzfxetr7yeq...@mail.gmail.com> > > | true > | a=$? b=`exit 1` b=$? >`echo /dev/null; exit 2` > | echo $? $a $b > > | Now, I wonder, what did I miss? > > That $? (the exit status) is defined only when a command completes. > What it is in the middle of a command execution isn't specified. > > | Where does it say in the standard that > | the value of parameter `?' is affected by redirections, > > It isn't the redirection, but the command substitution that generates > the file name for the redirection. > > | and that its > | value depends on assignments that appear earlier in the same command? > > All this stuff is just unspecified, the order in which all of this is > carried out, and precisely when $? gets updated, isn't specified, if you > want to achieve meaningful results, you need to split the one > multi-assignemnt > with redirect command into multiple commands. > > You get 1 0 0 from a shell which only sets $? when a command completes > (and which does the redirect before the arg expansions). > > Getting 2 for $? comes because it all depends which of the two command > substitutions is executed first (the last one executed provides $?), which > depends upon whether the redirect happens first or the arg expansions, and > for a command with no actual command word, that's unspecified > (implementations > are allowed to do it either way - which the standard allows, as as you see, > different implementations do it different ways, and users need to be aware > of that). > > Getting a non-zero value for a or b just means that $? is being internally > updated when a value for it becomes available, rather than only when a > command completes, about which as best I remember, nothing is said in the > standard at all. > Oh, okay then. Thanks > kre > > -- Oğuz
