Docco
$ man bash ... CONDITIONAL EXPRESSIONS ... -a file True if file exists. -e file True if file exists. ... 'May be' would be nice for newbies to precise which options are [ specific vs [[ specific for instance -a file True if file exists ([[ only, for [ see test builtin) This to avoid things like $ [ -a /tmp ] && echo ok || echo nok ok $ [ ! -a /tmp ] && echo ok || echo nok ok I know it is obvious, unless this is intended to force a complete multi-pass man read...
Re: Docco
On Wed, Mar 27, 2024 at 10:00:06AM +0100, Phi Debian wrote: > $ man bash > ... > CONDITIONAL EXPRESSIONS > ... > >-a file > True if file exists. >-e file > True if file exists. > ... > > 'May be' would be nice for newbies to precise which options are [ specific > vs [[ specific for instance > >-a file > True if file exists ([[ only, for [ see test builtin) > > This to avoid things like > > $ [ -a /tmp ] && echo ok || echo nok > ok > $ [ ! -a /tmp ] && echo ok || echo nok > ok > > I know it is obvious, unless this is intended to force a complete > multi-pass man read... Would it not be untrue to say that "-a" is specific to "[[", as it is clearly not the case? The fact that it is easy to confuse the two is a different matter, but the documentation is correct for the current implementation (which mimics the ksh shell with regards to the unary "-a" operator). -- Andreas (Kusalananda) Kähäri Uppsala, Sweden .
Re: Docco
On Wed, Mar 27, 2024 at 10:28 AM Andreas Kähäri wrote: > On Wed, Mar 27, 2024 at 10:00:06AM +0100, Phi Debian wrote: > > $ man bash > > Would it not be untrue to say that "-a" is specific to "[[", as it is > clearly not the case? The fact that it is easy to confuse the two is > a different matter, but the documentation is correct for the current > implementation (which mimics the ksh shell with regards to the unary > "-a" operator). > > -- > Andreas (Kusalananda) Kähäri > Uppsala, Sweden > > . Ok may be my wording is not correct, but yet it require a good reading compile to get it right, first read all about [[ that is at the top of the man (at 5%), then get the 'CONDITIONAL EXPRESSIONS' distingo between [[ vs [ (at 40%) and finally get to 'test expr' (at 92%) to discover the whole thing about -a vs -e (same for other options), a little heads up when quick reading directly at 'CONDITIONAL EXPRESSIONS' would not hurt and not jeopardise the docco semantic I guess?
Re: Docco
Interestingly, the ksh docco say that 'Conditional Expressions' applies to [[ only :-) and then say the -a is obsolete. test expression later says the -a and -o binary oper- ators can be used, but they are fraught with pitfalls due to grammatical ambiguities and therefore deprecated in favor of in- voking separate test commands Ok let's forget about this...
Re: Docco
On Wed, Mar 27, 2024 at 10:00:06AM +0100, Phi Debian wrote:
> $ man bash
> ...
> CONDITIONAL EXPRESSIONS
> ...
>
>-a file
> True if file exists.
>-e file
> True if file exists.
> ...
>
> 'May be' would be nice for newbies to precise which options are [ specific
> vs [[ specific for instance
>
>-a file
> True if file exists ([[ only, for [ see test builtin)
>
> This to avoid things like
>
> $ [ -a /tmp ] && echo ok || echo nok
> ok
> $ [ ! -a /tmp ] && echo ok || echo nok
> ok
>
> I know it is obvious, unless this is intended to force a complete
> multi-pass man read...
I wouldn't say it's "obvious" what's happening here. The problem is
that there are two different "-a" operators, one unary, and one binary.
"help test" documents both of them:
hobbit:~$ help test | grep -- -a
-a FILETrue if file exists.
EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
In your first example, you are using the unary -a operator on a file:
> $ [ -a /tmp ] && echo ok || echo nok
> ok
This one returns true because there are two arguments, and the first one
is not '!', and is a "unary primary" (POSIX wording). Therefore it uses
the unary -a and tests for existence of the second argument as a file.
In your second example, you are using the binary -a operator:
> $ [ ! -a /tmp ] && echo ok || echo nok
> ok
Here, you have three arguments, and argument 2 is a "binary primary"
(POSIX wording again), so it's treated as if you had written this:
[ ! ] && [ /tmp ] && echo ok || echo nok
This is simply performing two string length tests. Both strings are
non-empty (the first is one character, and the second is four), so
the result is true.
The check for whether the first argument is '!' is not performed,
because the "$2 is a binary primary" check comes first. This is how
POSIX documents it.
So... how do you work around this? Well, the easiest way would be
to stop using -a entirely. Both the unary *and* binary forms. The
unary form can be replaced by -e, and then everything works as you
expect. The binary form should be discarded along with "-o", and
never used. You are much better off stringing together multiple
test or [ commands instead:
if [ -e "$logdir" ] && [ -e "$outputdir" ]; then ...
This removes all ambiguity, and is in fact the only supported way
to write this under POSIX restrictions (">4 arguments: The results
are unspecified.")
Re: Docco
On Mär 27 2024, Greg Wooledge wrote: >> $ [ ! -a /tmp ] && echo ok || echo nok >> ok > > Here, you have three arguments, and argument 2 is a "binary primary" > (POSIX wording again), so it's treated as if you had written this: > > [ ! ] && [ /tmp ] && echo ok || echo nok > > This is simply performing two string length tests. Both strings are > non-empty (the first is one character, and the second is four), so > the result is true. > > The check for whether the first argument is '!' is not performed, > because the "$2 is a binary primary" check comes first. This is how > POSIX documents it. FWIW, ksh parses it the other way round: $ ksh93 -c '[ ! -a /tmp ]; echo $?; [ . -a /tmp ]; echo $?; [ - -a /tmp ]; echo $?' 1 0 ksh93: [: -: unknown operator 2 -- Andreas Schwab, SUSE Labs, sch...@suse.de GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7 "And now for something completely different."
Re: Docco
On 3/27/24 5:00 AM, Phi Debian wrote: $ man bash ... CONDITIONAL EXPRESSIONS ... -a file True if file exists. -e file True if file exists. ... 'May be' would be nice for newbies to precise which options are [ specific vs [[ specific for instance All the unary and binary primaries described there are available with both `[[' and `test'. -a file True if file exists ([[ only, for [ see test builtin) This would not be accurate. `-a' is deprecated but still accepted as a unary primary. This to avoid things like $ [ -a /tmp ] && echo ok || echo nok ok $ [ ! -a /tmp ] && echo ok || echo nok ok `test' works on the number of arguments, so these can be expected to be different. I know it is obvious, unless this is intended to force a complete multi-pass man read... The [[ and test descriptions document the differences. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
Re: Docco
On 3/27/24 5:50 AM, Phi Debian wrote: Ok may be my wording is not correct, but yet it require a good reading compile to get it right, first read all about [[ that is at the top of the man (at 5%), then get the 'CONDITIONAL EXPRESSIONS' distingo between [[ vs [ (at 40%) and finally get to 'test expr' (at 92%) to discover the whole thing about -a vs -e (same for other options), a little heads up when quick reading directly at 'CONDITIONAL EXPRESSIONS' would not hurt and not jeopardise the docco semantic I guess? This is from the first paragraph of CONDITIONAL EXPRESSIONS: "The test and [ commands determine their behavior based on the number of arguments; see the descriptions of those commands for any other command-specific actions." The texinfo manual has internal cross-references; the man page format is not that flexible. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
Re: Docco
On 3/27/24 7:40 AM, Andreas Schwab wrote: The check for whether the first argument is '!' is not performed, because the "$2 is a binary primary" check comes first. This is how POSIX documents it. FWIW, ksh parses it the other way round: $ ksh93 -c '[ ! -a /tmp ]; echo $?; [ . -a /tmp ]; echo $?; [ - -a /tmp ]; echo $?' 1 0 ksh93: [: -: unknown operator 2 Bash uses the order POSIX specifies. -a and -o are binary primaries when test gets three arguments. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
Re: Memory Leak - Bash 4.3.x30
On 3/26/24 1:33 PM, Jordi Ferrer wrote:
Just in case for people running old servers:
This simple code cause a memory leak in bash:
#!/bin/bash
#
Array=("S" "E")
while [ 1 ]; do
A=${Array[0]}
done
This was fixed by patch 40 to bash-4.3; if you're running a fully-patched
version you won't encounter it.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
