The dot

Why do I have to prefix the program with "./" to run it, sometimes, and sometimes not?

  dlink@viddev1> hello.sh
  -bash: hello.sh: command not found

  dlink@viddev1> ./hello.sh
  Hello, World.

It has to do with your PATH environment variable.

Let's look at the value of $PATH:

  dlink@viddev1> echo $PATH
  /usr/local/qt/bin:/usr/local/pgsql813/bin:/home/dlink/bin:/usr/local
  /bin:/usr/bin:/usr/X11R6/bin:/bin:/usr/games:/opt/gnome/bin:/opt/kde
  3/bin:/usr/lib/java/jre/bin:/usr/local/bin:/home/dlink/bin:/opt/gnom
  e/bin:/home/dlink/video/bin:/home/dlink/globalvideo/bin

The shell searches for the program in each of the (colon separated) subdirectories listed.

One nice way to examine the $PATH is to replace colons with carriage returns:

  dlink@viddev1> echo $PATH | tr ':' '\n'
  /usr/local/qt/bin
  /usr/local/pgsql813/bin
  /home/dlink/bin
  /usr/local/bin
  /usr/bin
  /usr/X11R6/bin
  /bin
  /usr/games
  /opt/gnome/bin
  /opt/kde3/bin
  /usr/lib/java/jre/bin
  /usr/local/bin
  /home/dlink/bin
  /opt/gnome/bin
  /home/dlink/video/bin
  /home/dlink/globalvideo/bin

Where am I?

  dlink@viddev1> pwd
  /home/dlink/public_html/bash_scripting

Oh, and that subdirectory is not in the $PATH list.

That is why it does not work when i don't use the ./ !

The dot (.) is actually just a relative path to the file.

The dot (.) means current working directory.

Dot dot (..) means the parent directory.

You can add the dot (.) to your PATH if you like:

  dlink@viddev1> PATH=".:$PATH"
  dlink@viddev1> echo $PATH | tr ':' '\n'
  .
  /usr/local/qt/bin
  /usr/local/pgsql813/bin
  /home/dlink/bin
  /usr/local/bin
  /usr/bin
  /usr/X11R6/bin
  /bin
  /usr/games
  /opt/gnome/bin
  /opt/kde3/bin
  /usr/lib/java/jre/bin
  /usr/local/bin
  /home/dlink/bin
  /opt/gnome/bin
  /home/dlink/video/bin
  /home/dlink/globalvideo/bin

  dlink@viddev1> hello.sh
  Hello, World.

  dlink@viddev1> ./hello.sh
  Hello, World.