Question

Can anybody tell me what will this script do? What is the -z on the 3rd line?

  Filename=File.txt
  X=`ls /home/$Filename`
  if [ -z "$X" ]; then
  exit
  fi

Answer 1

Filename=File.txt

The $Filename variable now has the value File.txt.

X=`ls /home/$Filename`

The $X variable now contains the output of the command ls /home/File.txt. If the file exists, it will contain something, otherwise it will be an empty string.

if [ -z "$X" ]; then

If the value of the variable $X is an empty string (meaning that /home/File.txt does not exist, otherwise $X would contain something), then:

  exit
fi

---

This is a pretty awkward way of writing:

if ! [ -e "/home/File.txt" ]; then exit; fi

-e returns true if the path exists. You can also check for files (-f), directories (-d), symbolic links (-L), etc. Take a look at man [ for more options that can be used with [. You’ll also find -z there:

-z string True if the length of string is zero.