Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
#!/bin/bash
# 'getopts' processes command line arguments to script.
# The arguments are parsed as "options" (flags) and associated arguments.
# Try invoking this script with
# 'scriptname −mn'
# 'scriptname −oq qOption' (qOption can be some arbitrary string.)
# 'scriptname −qXXX −r'
#
# 'scriptname −qr' − Unexpected result, takes "r" as the argument to option "q"
# 'scriptname −q −r' − Unexpected result, same as above
# If an option expects an argument ("flag:"), then it will grab
# whatever is next on the command line.
NO_ARGS=0
E_OPTERROR=65
if [ $# −eq "$NO_ARGS" ] # Script invoked with no command−line args?
then
echo "Usage: `basename $0` options (−mnopqrs)"
exit $E_OPTERROR # Exit and explain usage, if no argument(s) given.
fi
# Usage: scriptname −options
# Note: dash (−) necessary
while getopts ":mnopq:rs" Option
do
case $Option in
m ) echo "Scenario #1: option −m−";;
n | o ) echo "Scenario #2: option −$Option−";;
p ) echo "Scenario #3: option −p−";;
q ) echo "Scenario #4: option −q−, with argument \"$OPTARG\"";;
# Note that option 'q' must have an associated argument,
# otherwise it falls through to the default.
r | s ) echo "Scenario #5: option −$Option−"'';;
* ) echo "Unimplemented option chosen.";; # DEFAULT
esac
done
shift $(($OPTIND − 1))
# Decrements the argument pointer so it points to next argument.
exit 0
Script Behavior
source, . (dot command)
This command, when invoked from the command line, executes a script. Within a script, a source
file−name loads the file file−name. This is the shell scripting equivalent of a C/C++
#include directive. It is useful in situations when multiple scripts use a common data file or
function library.
Example 11−18. "Including" a data file
#!/bin/bash
Chapter 11. Internal Commands and Builtins 139