Check for existence (style question)

Wednesday 2 July 2008 13:33, RValentinFischer wrote:

I would like to test, whether a directory mydir contains at least one
file which has abc in its name.
This is one way to do it on Solaris ( Linux, the option used on
fgrep must be -q):
>
if { ls mydir | fgrep -s abc }
then
: # yes, one or more files with names containing abc exist in mydir
fi
>
But I don't like this solution. First, it is not portable between
Solaris and Linux.

It is, if you use "grep -F -q" instead of fgrep.

Second, it looks
to me overly complicated.
>
Is there a nicer way this can be done entirely within bash or zsh?
bash would be preferred
because I'm supposed to use bash for the task, so I would need to have
compelling reasons
for using zsh.

A (really) ugly trick with bash would probably be

shopt -s nullglob
for i in *abc*; do
# your code here
break;
done

But if you're worried about style, then the above code most certainly won't
fit your needs :-)

--
All the commands are tested with bash and GNU tools, so they may use
nonstandard features. I try to mention when something is nonstandard (if
I'm aware of that), but I may miss something. Corrections are welcome.

I would like to test, whether a directory mydir contains at least one
file which has abc in its name.
This is one way to do it on Solaris ( Linux, the option used on
fgrep must be -q):

if { ls mydir | fgrep -s abc }
then
: # yes, one or more files with names containing abc exist in mydir
fi

But I don't like this solution. First, it is not portable between
Solaris and Linux. Second, it looks
to me overly complicated.

Is there a nicer way this can be done entirely within bash or zsh?
bash would be preferred
because I'm supposed to use bash for the task, so I would need to have
compelling reasons
for using zsh.

Ronald

RValentinFischer wrote:
I would like to test, whether a directory mydir contains at least one
file which has abc in its name.
This is one way to do it on Solaris ( Linux, the option used on
fgrep must be -q):
>
if { ls mydir | fgrep -s abc }
then
: # yes, one or more files with names containing abc exist in mydir
fi
>
But I don't like this solution. First, it is not portable between
Solaris and Linux. Second, it looks
to me overly complicated.
>
Is there a nicer way this can be done entirely within bash or zsh?
bash would be preferred
because I'm supposed to use bash for the task, so I would need to have
compelling reasons
for using zsh.
Hmm, maybe this:
for f in *abc*; do [ "$f" != '*abc*' ] && echo Yes; break; done

Bye, Jojo

RValentinFischer wrote:
I would like to test, whether a directory mydir contains at least one
file which has abc in its name.
This is one way to do it on Solaris ( Linux, the option used on
fgrep must be -q):
>
if { ls mydir | fgrep -s abc }
then
: # yes, one or more files with names containing abc exist in mydir
fi
>
But I don't like this solution. First, it is not portable between
Solaris and Linux. Second, it looks
to me overly complicated.

If you want to keep the if/ls pattern and don't mind redirection of
irrelevant output

if ls mydir/*abc* >/dev/null 2>&1
then
echo yes
fi



set - mydir/*abc*
[ -f "$1" ] && echo Yes

It surely depends what one considers complicated. Is using a pipe
and two external processes complicated? Is using only standard shell
features complicated? You decide.

Janis

>
Is there a nicer way this can be done entirely within bash or zsh?
bash would be preferred
because I'm supposed to use bash for the task, so I would need to have
compelling reasons
for using zsh.
>
Ronald

Wednesday 2 July 2008 21:16, bsh wrote:

>set - mydir/*abc*
>[ -f "$1" ] && echo Yes
>
This is not a determinate test. If there is a file named
"*abc*", this test will also fail.

No, since '*abc*' is a valid expansion for *abc*, after all.

--
All the commands are tested with bash and GNU tools, so they may use
nonstandard features. I try to mention when something is nonstandard (if
I'm aware of that), but I may miss something. Corrections are welcome.