Hi,

Usually, to test the return of a command (success or failure), I use a
sequence of two instructions: the instruction, and then the if test:

$ touch bar
$ ls bar
$ if [ "$?" = 0 ];then echo success;fi
success

I would like to run the command between the brackets: is this possible?
The following command does not seem to work:

$ if [ `ls bar 1>/dev/null 2>&1` ];then echo success;fi

Thanks in advance

Julien
--
"Allez, Monsieur, allez, et la foi vous viendra." (D'Alembert).

> I would like to run the command between the brackets: is this possible?
> The following command does not seem to work:
>
> $ if [ `ls bar 1>/dev/null 2>&1` ];then echo success;fi

ls bar >/dev/null 2>&1 && echo success || echo failure


Regards
Dimitre

>> I would like to run the command between the brackets: is this possible?
>> The following command does not seem to work:
>>
>> $ if [ `ls bar 1>/dev/null 2>&1` ];then echo success;fi
>
> ls bar >/dev/null 2>&1 && echo success || echo failure

If you just want to check if the file exists:

[ -e bar ] && echo success || echo failure


Regards
Dimitre

On Sun, 05 Nov 2006 16:39:22 +0100, Tribulations Parallèles
<Tribulations@Paralleles.invalid> wrote:
> Hi,
>
> Usually, to test the return of a command (success or failure), I use a
> sequence of two instructions: the instruction, and then the if test:
>
> $ touch bar
> $ ls bar
> $ if [ "$?" = 0 ];then echo success;fi
> success
>
> I would like to run the command between the brackets: is this possible?
> The following command does not seem to work:
>
> $ if [ `ls bar 1>/dev/null 2>&1` ];then echo success;fi
>
You don't need brackets. The left bracket itself is a command, a
synonym for "test". (when it's called '[' it requires a ']')

if ls bar 1>/dev/null 2>&1; then echo success; fi

You could also write
if [ -e bar ]; then echo success; fi

By the way, `ls bar 1>/dev/null 2>&1` results in an empty string, which
evaluates as false inside [ ].


--
When asked by an anthropologist what the Indians called America before
the white men came, an Indian said simply "Ours."
-- Vine Deloria, Jr.

2006-11-05, 16:39(+01), Tribulations Parallèles:
> Hi,
>
> Usually, to test the return of a command (success or failure), I use a
> sequence of two instructions: the instruction, and then the if test:
>
> $ touch bar
> $ ls bar
> $ if [ "$?" = 0 ];then echo success;fi
> success
>
> I would like to run the command between the brackets: is this possible?
> The following command does not seem to work:
>
> $ if [ `ls bar 1>/dev/null 2>&1` ];then echo success;fi
[...]

if ls -d bar > /dev/null 2>&1; then echo success; fi

if relies on the exit status of the list of commands inbetween
"if" and "then" to decide whether to run the "then" command list
or the "else" command list.

"[" is just another command. "[ "$?" -eq 0 ]" is a noop as it
just asks the "[" command to replicate the exit status (at least
the meaning of the exit status) from the previously run command.

IOW, in

cmd
if [ "$?" -eq 0 ]; [ "$?" -eq 0 ]; [ "$?" -eq 0 ]; then...

All the "[" commands are useless as they just perpetrate $?. It
should be:

if cmd; then

[ "$?" -eq 0 ] sets $? to 0 if $? was 0 and $? to 1 if it wasn't
0. Another way to perpetrate $?, could be (exit "$?"), that is
start a subshell and make it exit with the $? exit status.
Again, not very useful.

--
Stéphane

Radoulov, Dimitre wrote:

>> I would like to run the command between the brackets: is this possible?
>> The following command does not seem to work:
>>
>> $ if [ `ls bar 1>/dev/null 2>&1` ];then echo success;fi
>
> ls bar >/dev/null 2>&1 && echo success || echo failure

Thanks a lot, it works. But is it possible to keep the ls instruction in a
if instruction?

Indeed, if there is a lot of instructions to execute in case of success, I
am compelled to use parenthesis:

ls bar 1>/dev/null 2>&1 && (
echo success
echo foo
echo coco
) ||
echo failure

It works, but I am used to using "if" instruction, so I just want to know if
it could be possible to keep the classical construction.

Julien

--
"Allez, Monsieur, allez, et la foi vous viendra." (D'Alembert).

[...]
> Indeed, if there is a lot of instructions to execute in case of success, I
> am compelled to use parenthesis:
>
> ls bar 1>/dev/null 2>&1 && (
> echo success
> echo foo
> echo coco
> ) ||
> echo failure
>
> It works, but I am used to using "if" instruction, so I just want to know
> if
> it could be possible to keep the classical construction.
[...]

if ls bar > /dev/null 2>&1 ; then
echo success
echo foo
echo coco
fi


Regards
Dimitre

2006-11-5, 11:00(-05), Bill Marcum:
[...]
> You don't need brackets. The left bracket itself is a command, a
> synonym for "test". (when it's called '[' it requires a ']')
>
> if ls bar 1>/dev/null 2>&1; then echo success; fi
>
> You could also write
> if [ -e bar ]; then echo success; fi

It should be noted though that the two commands above are not
equivalent if "bar" is a directory or a symbolic link whose
target we can't determine the existence.

> By the way, `ls bar 1>/dev/null 2>&1` results in an empty string, which
> evaluates as false inside [ ].
[...]

Actually, as it is not quoted, it results in no argument at all
(which is not the same thing as an empty argument) but in any
case, "[" returns false for both [ ] and [ "" ].

--
Stéphane