Shell Programming for System Administrators SA-245

Prerequisites:

• Use basic UNIX commands, such as rm, cp, man, more, mkdir, ps, and chmod
• Create and edit text files in vi or a text editor

Objectives:

• Use flow control constructs, such as branching and looping
• Customize system-wide shell initialization files
• Use local and environmental variables and shell metacharacters in scripts
• Use the exit status of a command to determine if the command succeeded or failed
• Develop interactive scripts
• Write a script that uses functions
• Write a script that uses a trap to catch a signal
• Access and process command-line arguments passed into a script
• Write sed scripts to perform noninteractive editing tasks
• Write nawk scripts to manipulate individual fields within a record
• Write nawk scripts to write reports based upon an input file
• Perform string manipulation and integer arithmetic on shell variables
• Write real world administration and reporting scripts
• Use regular expressions with the grep, sed, and nawk
• Manipulate text files with grep, sed, and nawk

Topics:

UNIX Shells and Shell Scripts

• Describe the role of shells in the UNIX environment
• Describe the standard shells
• Define the components of a shell script
• Write a simple shell script

Writing and Debugging Scripts

• Start a script with #!
• Put comments in a script
• Change permissions on a script
• Execute a script
• Debug a script

The Shell Environment

• Use Bourne and Korn shell variables
• Assign values to shell variables
• Unset shell and environment variables
• Customize the user environment using the .profile file
• Perform arithmetic operations
• Create and use aliases
• Customize the Bourne and Korn shell environments
• Use the tilde expansion and command substitution features of the Korn shell

Regular Expressions and the grep Command

• Use and describe regular expressions
• Describe the grep command
• Use the grep command to find patterns in a file
• Use the regular expression characters with the grep command

The sed Editor

• Use the sed editor to perform noninteractive editing tasks
• Use regular expression characters with the sed command

The nawk Programming Language

• Use nawk commands from the command line
• Write simple nawk programs to generate data reports from text files
• Write simple nawk programs to generate numeric and text reports from text files

Conditionals

• Use the exit status of a command as conditional control
• Use the "if" statement to test a condition
• Pass values using command-line arguments (positional parameters) into a script
• Create USAGE messages
• Use conditional if, then, elif, else, and fi constructs
• Use exit, let, and test statements ([[ ]], " ")
• Apply the , ||, and ! Boolean logic operators
• Use the case statement

Interactive Scripts

• Use the print and echo commands to display text
• Use the read command to interactively assign data to a shell variable
• Read user input into one or more variables, using one read statement
• Use special characters, with print and echo, to make the displayed text more user friendly
• Create a "here" document
• Use file descriptors to read from and write to multiple files

Loops

• Write scripts that use for, while, and until loops
• Write a script using the select statement
• Describe when to use loops within a script
• Generate argument lists using command, variable, and file-name substitution

The getopt Statement

• Process script options using the getopts statement

Advanced Variables, Parameters, and Argument Lists

• Declare strings, integers, and array variables
• Manipulate string variables
• Change the values of the positional parameters using the set statement within a script
• Use Korn shell arrays
• Set default values for parameters
• Use the Korn shell built-in let, print, set, and typeset statements

Functions

• Create user-defined functions in a shell script
• Create, invoke, and display functions from the command line
• Pass arguments into a function
• Call functions from special (function) files that are saved in one or more function directories
• Describe where functions are available for use