Re: [Help-bash] Unexpected behaviour in job control inside subshell environment

[Diego Augusto Molina]

El 01/12/16 a las 13:29, Greg Wooledge escribió:
> On Thu, Dec 01, 2016 at 12:55:04PM -0300, Diego Augusto Molina wrote:
> > So I came up with the following idea:
> >
> > SLEEP_ARG=wrong-value;
> > (
> >   sleep "10${SLEEP_ARG}" &
> >   sleep 0.1; # Optional but recommended
> >   jobs -r 1;
>
> Remember that job control is disabled in scripts (non-interactive shells)
> by default.

Great point, but I'm using an interactive shell.

> As far as wrapping the sleep(1) command to validate arguments, I would
> go with something more like this:
>
> ver=$(sleep --version 2>&1)
> if [[ $ver = *GNU* ]]; then
>   : fractions are allowed
> else
>   : fractions are probably going to blow up
> fi
>
> Actually *calling* sleep(1) with wacky arguments to see how long it
> takes to die is pretty suboptimal, I should think.

The reason of the original mail was to understand why the code didn't 
work as expected. It wasn't intended to ask for a solution to the 
problem of validating the argument given to the "sleep" program. The 
real solution I came up to is:

SLEEP_TIME=something;
sleep_time_regex='^(\.[0-9]+)?$';
if
  [ -z "$SLEEP_TIME" ] || # SLEEP_TIME must be a value
  ( # If we don't have the GNU implem, only integers are accepted
    [[ "$(sleep --version 2>&1;)" != *GNU* ]] &&
    [ -n "${SLEEP_TIME##*([0-9])}" ]
  ) || # If we do have the GNU implem, then we may have decimal point
  [[ ! "${SLEEP_TIME##*([0-9])}" =~ ${sleep_time_regex} ]];
then
  echo "Invalid SLEEP_TIME value.";
fi;

Note that I use a separate variable for the regex since the code won't 
run on a (very) old Bash implementation I'm testing with.