Trying to find out if a file or a directory exists within a shell program is pretty easy. You may also want to test if the directory is a symlink or if the file is executable. Here are a few tips to perform some various validation tasks.

Checking if the directory exists:

if [ -d $DIR ]; then
   echo "Is a directory."
else
   echo "Not a directory."
fi

Checking if the directory is a symbolic link:

if [ -d $DIR ]; then
   if [ -L $DIR ]; then
      echo "Is a symbolic link."
   else
      echo "Not a symbolic link."
   fi
else
   echo "Not a directory."
fi

Checking if the file exists:

if [ -e $FILENAME ]; then
   echo "Is a file."
else
   echo "Not a file."
fi

Checking if the file is a symbolic link:

if [ -e $FILENAME ]; then
   if [ -L $FILENAME ]; then
      echo "Is a symbolic link."
   else
      echo "Not a symbolic link."
   fi
else
   echo "Not a file."
fi

Checking if the file is executable:

if [ -e $FILENAME ]; then
   if [ -x $FILENAME ]; then
      echo "Is a executable."
   else
      echo "Not executable."
   fi
else
   echo "Not a file."
fi

There are a number of other parameters to use to perform more tests. On most unix systems you can run “man test” from the command line to get help.

Here is the manpage from a debian linux system.

       -z STRING
              the length of STRING is zero

       STRING1 = STRING2
              the strings are equal

       STRING1 != STRING2
              the strings are not equal

       INTEGER1 -eq INTEGER2
              INTEGER1 is equal to INTEGER2

       INTEGER1 -ge INTEGER2
              INTEGER1 is greater than or equal to INTEGER2

       INTEGER1 -gt INTEGER2
              INTEGER1 is greater than INTEGER2

       INTEGER1 -le INTEGER2
              INTEGER1 is less than or equal to INTEGER2

       INTEGER1 -lt INTEGER2
              INTEGER1 is less than INTEGER2

       INTEGER1 -ne INTEGER2
              INTEGER1 is not equal to INTEGER2

       FILE1 -ef FILE2
              FILE1 and FILE2 have the same device and inode numbers

       FILE1 -nt FILE2
              FILE1 is newer (modification date) than FILE2

       FILE1 -ot FILE2
              FILE1 is older than FILE2

       -b FILE
              FILE exists and is block special

       -c FILE
              FILE exists and is character special

       -d FILE
              FILE exists and is a directory

       -e FILE
              FILE exists

       -f FILE
              FILE exists and is a regular file

       -g FILE
              FILE exists and is set-group-ID

       -G FILE
              FILE exists and is owned by the effective group ID

       -h FILE
              FILE exists and is a symbolic link (same as -L)

       -k FILE
              FILE exists and has its sticky bit set

       -L FILE
              FILE exists and is a symbolic link (same as -h)

       -O FILE
              FILE exists and is owned by the effective user ID

       -p FILE
              FILE exists and is a named pipe

       -r FILE
              FILE exists and read permission is granted

       -s FILE
              FILE exists and has a size greater than zero

       -S FILE
              FILE exists and is a socket

       -t FD  file descriptor FD is opened on a terminal

       -u FILE
              FILE exists and its set-user-ID bit is set

       -w FILE
              FILE exists and write permission is granted

       -x FILE
              FILE exists and execute (or search) permission is granted

       Except for -h and  -L,  all  FILE-related  tests  dereference  symbolic
       links.   Beware  that  parentheses  need  to be escaped (e.g., by back-
       slashes) for shells.  INTEGER may also be -l STRING, which evaluates to
       the length of STRING.

Enjoy