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(1) What is a shell script

• A text file containing commands which could have been typed directly into the shell.

  There is no difference in syntax between interactive command line use and placing the commands in a file. Some commands are only useful when used interactively (e.g. command line history recall) and other commands are too complex to use interactively.

• The shell itself has limited capabilities -- the power comes from using it as a "glue" language to combine the standard Unix utilities, and custom software, to produce a tool more useful than the component parts alone.

• Any shell can be used for writing a shell script. To allow for this, the first line of every script is:
  #!/path/to/shell (e.g. #!/bin/ksh).

  The #! characters tell the system to locate the following pathname, start it up and feed it the rest of the file as input. Any program which can read commands from a file can be started up this way, as long as it recognizes the # comment convention. The program is started, and then the script file is given to it as an argument. Because of this, the script must be readable as well as executable. Examples are perl, awk, tcl and python.

• Any file can be used as input to a shell by using the syntax:
  ksh myscript

• If the file is made executable using chmod, it becomes a new command and available for use (subject to the usual $PATH search).
  chmod +x myscript

Example: ex0 display, text