On Fri, 19 Mar 2021 23:26:01 +0100
Pierre Labastie <pierre.labas...@neuf.fr> wrote:
> On Fri, 2021-03-19 at 07:24 -0400, Scott Andrews wrote:
> > On Fri, 19 Mar 2021 07:09:06 +0100
> > Pierre Labastie <pierre.labas...@neuf.fr> wrote:
> >
> > >
> > > Using brackets depends on "something". If something is a
> > > predicate, you need brackets. If something is a (compound)
> > > command, no brackets. I've not looked in details at the "if" in
> > > the boot scripts, but they must be correct in this respect,
> > > since they seem to work...
> > >
> >
> > By brackets are you talking about [ ] or [[ ]]?
> >
> > if [ something ]; then this; fi,
> >
> > Really means
> >
> > if test something; then this; fi
> >
> > [ is actually test, and the [ must be followed by ]
> >
> > [[ ]] is an expression
> >
> > See the gnu bash reference manual for clarification.
> >
>
> Here is an experiment:
> ---
> pierre [ ~ ]$ toto () {
> > return 1
> > }
> pierre [ ~ ]$ if toto; then echo true; else echo false; fi
> false
> pierre [ ~ ]$ if [ toto ]; then echo true; else echo false; fi
> true
> ---
>
> Pierre
>
Here is a more complete test:
toto () {
return 1
}
gogo () {
return 0
}
echo "toto test"
if toto; then echo true; else echo false; fi
if [ toto ]; then echo true; else echo false; fi
if test toto; then echo true; else echo false; fi
if [[ toto ]]; then echo true; else echo false; fi
echo "gogo test"
if gogo; then echo true; else echo false; fi
if [ gogo ]; then echo true; else echo false; fi
if test gogo; then echo true; else echo false; fi
if [[ gogo ]]; then echo true; else echo false; fi
Results:
toto test
false
true
true
true
gogo test
true
true
true
true
Here is what the gnu bash manual states:
test
[
test expr
Evaluate a conditional expression expr and return a status of 0
(true) or 1 (false). Each operator and operand must be a separate
argument. Expressions are composed of the primaries described below
in Section 6.4 [Bash Conditional Expressions], page 92. test does not
accept any options, nor does it accept and ignore an argument of --
as signifying the end of options. When the [ form is used, the last
argument to the command must be a ].
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