Can I avoid this subshell in a POSIX sh script?

Question

I am trying to comprehend how, if even it can be done, can I avoid subshell?

Is this the only way the code can be written or is there another way?

I tried to use braces { ... }, but it won't pass shellcheck and won't run.

is_running_interactively ()
# test if file descriptor 0 = standard input is connected to the terminal
{
    [ -t 0 ]
}

is_tput_available ()
# check if tput coloring is available
{
    command -v tput > /dev/null 2>&1 &&
    tput bold > /dev/null 2>&1 &&
    tput setaf 1 > /dev/null 2>&1
}

some_other_function ()
# so far unfinished function
{
    # is this a subshell? if so, can I avoid it somehow?
    ( is_running_interactively && is_tput_available ) || # <-- HERE
    {
        printf '%b' "${2}"
        return
    }
    ...
}

oguz ismail · Accepted Answer · 2019-04-28T07:44:25.810

2

It is a compound-list, and yes those commands are run in a subshell. To avoid it, use curly braces instead of parentheses:

{ is_running_interactively && is_tput_available; } || ...

edited Apr 28 '19 at 07:44

answered Apr 28 '19 at 07:24

oguz ismail

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1

Oh, I see there needs to be a semi-colon, Thank you. – Vlastimil Burián Apr 28 '19 at 07:26
1

Actually *compound command* or technically a *compound list*. (see [POSIX Programmer's Guide](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_03) and 2-3 pages down for *compound-list* directly) – David C. Rankin Apr 28 '19 at 07:26
@David thanks, updated with correct term and link to the POSIX spec – oguz ismail Apr 28 '19 at 07:32
1

No problem. Good use of the brace-enclosed group `{...}` to avoid the subshell. – David C. Rankin Apr 28 '19 at 07:33

Can I avoid this subshell in a POSIX sh script?

1 Answers1