Scripting Syntax

Shell variables are not typed, meaning that you do not specify whether a variable is a string or a number (or whatever).

Variables are declared and assigned in one statement using the equal sign: for example,

counter = 0
custname = "Harold Davis"

If a string has no embedded spaces, you do not need to use quotation marks.

A $ is used to assign the contents of one variable to another: for example,

counter = $myvar

Using command-line parameters

• You can pass a shell script command-line parameters and retrieve them from inside the script. The first command-line parameter is referenced as $1, the second as $2, and so on.
  
  The following script illustrates how this works:
  
  

  # Display that command line _ 
    parameter 
  if [ $# -eq 0 ] 
  then 
    echo "Please provide a _     command line name!" 
  else 
    echo "Hello"  $1
  fi
  

  
  If you save this script as invoke and run it with no command-line parameters, the shell script asks, "Please provide a command line name!" Otherwise, the name you entered on the command line is echoed back (Figure 12.12).
  
  By the way, fi is not a typo—it is if spelled backward, and it represents the end of an if statement. In a similar fashion, case statements are ended with esac.
  
  In the script, $# is a built-in variable containing the number of command-line variables (see Table 12.1). The entry –eq is used to compare $# with 0 (see Table 12.2). The entry $1 represents the first command-line variable.
  
  

To accept interactive user input:

#! /bin/bash
# Interactive user input

echo "Enter your name:"
read yrname
echo "Is it time for tea, $yrname?"

chmod +x yrname