For loop to find out if directory exists in unix

Question

I want to use a script that checks whether a list of directories exists or not and at the same time it should print some custom message that I am sending.

For example:

I have a script that validates if directory exists or not:

**check.sh**

for i in $*
   if [ -d "$i" ]; then
      echo Found <msg-i> directory.
   else
       echo <msg-i> directory not found.

Now I want to call this script like this:

./check.sh $DIR1 msg1 $Dir2 msg2 $Dir3 msg3

So if DIR1 doesn't exist then I want to display message as "msg1 directory not found", similarly for DIR2 I want to show "msg2 directory not found". Here msg1 and msg2 are something I want to pass as string. How to achieve this? I am using bash shell.

Answer 1

Try this:

while [ -n "$1" ]
do
    dir="$1"
    msg="$2"
    if [ -d "$dir" ]; then
        echo "$msg dir FOUND"
    else
        echo "$msg dir NOT FOUND"
    fi
    shift 2
done

shift <n> command simply shifts left positional parameters passed to the script of n positions. For example if you call a script with:

./myscript 1 2 3 4

$1 is "1" and $2 is "2"

but if you shift 2 then $1 is "3" and $2 is "4".

In this way the loop consumes 2 parameters per cycle until $1 parameter is an empty string ( -n "$1").

while condition can be written more elegantly as:

while (( $# ))

obtaining the same result.

You can also check for the second parameter (while [ -n "$2" ]) but this changes the behavior when user provides an odd number of parameters:

• in the first case last directory will be checked but you'll have a strange message because $msg il empty
• il the second case you'll not have strange messages, but last directory will silently not be checked

Better test parameters at the beginning:

if (( $# % 2 ))
then
    echo "Provide an even number of parameters"
    exit 1
fi

Answer 2

Chepner Says:

The while condition can simply be (( $# )) (test if the number of positional parameters is non-zero).

Chaitanya Says:

Hi Chepner, thanks for providing alternate solution, can you please tell me how the while condition should actually look like in order to use $# , I tried different ways but it is not working for me.

Here's a quick sample:

while (( $# ))
do
   dir=$1
   msg=$2
   shift 2
   [...]
done

The while (( $# )) will be true as long as there are any command line arguments. Doing the shift twice removes arguments from the list. When no more arguments, the while loop ends.