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Re: Bash true/false builtings undocumented? "false" not working?

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On Fri, Aug 17, 2018 at 08:23:51AM -0400, Greg Wooledge wrote:
> On Fri, Aug 17, 2018 at 06:46:54PM +1000, Zenaan Harkness wrote:
> > $ test $? && echo ok || echo error $?
> 
> Others have already pointed out that  test $?  is not what you think it
> is.  When the test command is given 1 argument, it tests that argument's
> string length.  If the string length is 0, then it's false.  If the
> string length is non-zero, then it's true.
> 
> The string length of $? is always non-zero, so  test $?  is always true.

Exactly.

> But what I really wanted to point out is that the  x && y || z  construct
> is BROKEN and WRONG.  See <https://mywiki.wooledge.org/BashPitfalls#pf22>
> for the verbose explanation.

All generalizations suck :)

[...]

> Or, if you only care about one of the two cases, you may use EITHER
> the && or the || operator.  Just never, ever use both of them in the
> same compound command.
> 
> mycommand arg1 arg2 || die "whoopsie"

The construction

  foo && echo "bar" || echo "baz"

does probably work, because echo's exit status is (always?) 0 (the bash
builtin's documentation mumbles something about "write error"). And then,
the order matters -- first && then ||. I think such idiomatic constructions
are OK as long as you know what you're doing. As soon as the branches
contain more complex stuff, I agree you shouldn't do it: even if you've
convinced yourself that it works, the code becomes obscure and difficult
to understand/change by someone else (which might be yourself two years
down).

Cheers
- -- tomás
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Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-17 10:50 +0200
  Re: Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-17 11:00 +0200
  Re: Bash true/false builtings undocumented? "false" not working? Nicolas George <george@nsup.org> - 2018-08-17 11:00 +0200
    Re: Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-17 11:30 +0200
    Re: Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-17 11:40 +0200
      Re: Bash true/false builtings undocumented? "false" not working? Nicolas George <george@nsup.org> - 2018-08-17 11:40 +0200
      Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-17 12:20 +0200
      Re: Re: Bash true/false builtings undocumented? "false" not working? Clive Standbridge <list-user@tgstandbridges.plus.com> - 2018-08-17 14:10 +0200
        Re: Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-17 15:40 +0200
      Re: Bash true/false builtings undocumented? "false" not working? Greg Wooledge <wooledg@eeg.ccf.org> - 2018-08-17 14:30 +0200
        Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-17 15:50 +0200
          Re: Bash true/false builtings undocumented? "false" not working? Greg Wooledge <wooledg@eeg.ccf.org> - 2018-08-17 16:20 +0200
            Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-17 16:40 +0200
              Re: Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-18 01:10 +0200
        Re: Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-18 01:30 +0200
  Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-17 11:30 +0200
    Re: Bash true/false builtings undocumented? "false" not working? Zenaan Harkness <zenaan@freedbms.net> - 2018-08-17 11:40 +0200
      Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-17 11:50 +0200
        Re: Bash true/false builtings undocumented? "false" not working? tomas@tuxteam.de - 2018-08-17 12:00 +0200
      Re: Bash true/false builtings undocumented? "false" not working? Stefan Krusche <linux@stefan-krusche.de> - 2018-08-23 15:00 +0200
        Re: Bash true/false builtings undocumented? "false" not working? <tomas@tuxteam.de> - 2018-08-23 16:30 +0200

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