Programming the Shells

The basics of both the Bourne and the C shells have already been introduced. This chapter will concentrate on programming the shells.

All examples shown will use the Bourne shell. Most shell scripts are written in the Bourne shell because it is the only shell found on *ALL* UNIX systems. Scripts written in the Korn shell are gaining popularity.

C shell scripts are possible, but not recommended. Although the C shell is great for interactive work, it has many drawbacks in script programming.

• Introduction
  • Bourne - C shell comparisons
  • Variables
• A Simple Script
  • Running the Script
• Special Characters
  • '...': Turn off Meaning of Special Characters.
  • "...": Turn off Meaning of Special Characters EXCEPT $ and `
  • `...`: Use Output as Content of Variable
• Verbatim echo
• Parameters and the Shell
  • $0: The Name of the Invoking Command
  • $1 $2 $3 ... $9, $*: Shell Parameters
  • $#: Number of Parameters
  • shift: Shifts Parameters
• read: Reading Input from User
• test: Comparisons
  • Testing/Comparing Numbers
  • Verifying File Types
  • Comparing Strings
  • Combining test: Expressions
• Control Structures
  • for var in list
  • while condition
  • until loop
  • if statement
  • case: Selections
• expr: Doing Arithmetic
• Subroutines
• Miscellaneous
  • break
  • $$: Process ID
  • $!: PID (Process ID) of the previous background command
  • $: Return Code
  • A || B: Either or
  • A && B: Both or Nothing
  • set: Change Command-line Parameters
• trap: Trap signals
• Tips Using Shell Commands
  • basename: Current Directory
  • dirname: Directory Path
  • stty -echo: Passwords
  • cut, awk: Cut Selected Fields
• Exercises