May
26, 2003 -
Processing Shell Script Options with the
getopts Command
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The
getopts command simplifies the task of
validating and parsing command line
options and arguments for your shell
scripts. Without this built-in
command, writing shell script code to
perform these common tasks could quickly
become a complex and lengthy undertaking.
The syntax for the getopts command is as
follows:
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getopts
option-list variable
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option-list
contains valid options for the script, and
variable is set to the option if it is
found in option-list. If the option
is not in option-list, variable is set to
the "?" character.
The following snippet of code illustrates
a basic implementation of the command:
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#!/bin/ksh
PROG_NAME=$(basename $0)
A_FLAG=FALSE
B_FLAG=FALSE
while getopts abl: OPTION
do
case ${OPTION} in
a) A_FLAG=TRUE;;
b) B_FLAG=TRUE;;
l) LOGFILE=${OPTARG};;
\?) print -u2 "Usage: ${PROG_NAME} [
-a -b -l logfile_name ]"
exit 2;;
esac
done
print ${A_FLAG}
print ${B_FLAG}
print ${LOGFILE}
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There are a few
key points you should understand about
getopts and this example:
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- getopts
is designed to be executed inside of a
loop, processing one option each
iteration. Once getopts processes
the last option, it returns a non-zero
value and the loop terminates.
- options requiring an argument
("l" in this example) need to be
followed by a ":" (colon) on the
getopts command line.
- option arguments are stored in the
special variable OPTARG for script
processing.
- if an invalid option is used, correct
usage will be displayed and the script
will exit with a return code of 2.
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Here is a sample
of the output for the above code (the script
is named getopts_sample):
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# ./getopts_sample -a -b -l testlog.txt
TRUE
TRUE
testlog.txt
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You may want to
run the above code on your system to see
what happens when an invalid option is used.
The previous has been a basic introduction
to the getopts command. A more
detailed understanding can be obtained by
reviewing your shell's man page.
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