Shell Programming and Scripting

I want to be able to get all the directories in a path into a variable array, BUT if there ARE NO directories I want the Variable to be NULL and not echo any error message!

If there ARE directories, this will get the list of the directories whose name begins with the string "20":

Code:

DATE_DIRS=$(ls 20* -d)

And "ls 20* -d" entered at a command prompt will list the directories on the console.

But if there ARE NO directories then script or the command spits out the annoying error
"ls: cannot access 20*: No such file or directory"

How do I suppress the warning message?

Could try this - but be carefull that no files start with 20, you may want to check with [ -d $dir ] to trap any non-directories.

Code:

DATE_DIRS=$(ls -d 20* 2> /dev/null)

or

Code:

DATE_DIRS=$(echo 20*)
[ "$DATE_DIRS" = '20*' ] && DATE_DIRS=''

Thankyou,

The snipit

Code:

DATE_DIRS=$(ls -d 20* 2> /dev/null)

seams to do what I needed it to do.

So what exactly is going on here?

The ls is list, the '-d' filters for directories, and the 20* is the pattern the directories must match.... but what does the "2 > /dev/null" do ??

this is sending stderr to the /dev/null file. /dev/null is basically a black hole so in essence its just not sending any error messages to your screen.

Ahh, OK. Thankyou.

so in

Code:

"2 > /dev/null"

the "> /dev/null" uses the standard redirect into a "black hole" called "/dev/null" LOL.

How about the digit "2" ? Does the number "2" just kinda stands for "to", or does it hold some special meaning in this context?

the actual addition to the command is:

Code:

2> /dev/null

notice there is no space between the 2 and the >.

> means redirect standard output (stdout)
2> means redirect standard error (stderr)

and as your directing it into /dev/null it is written to a special file which discards anything sent to it.

you could do something like:

Code:

DATE_DIRS=$(ls -d 20* 2> /home/yourhome/error.out)

and then you can later see what error messages were sent from running the command but as you dont care /dev/null just discards the message for you.

Supper.

I understand it now.

Thanks for the details !

I can really understand why people both LOVE and HATE this langauge.

SO much fuctionality is packed into so few charecters - makes the code terse and fuctional, but hard to understand unless yon know the 'secret code" .