官术网_书友最值得收藏!

Passing your program flags

After going into your shell and opening a new file in your favorite editor, let's get started by creating a Bash script that does the following:

  • When no flags or arguments are specified, prints out a help message
  • When either the -h or --help flags are set, it prints out a help message
  • When the -f or --firstname flags are set, it sets the the first name variable
  • When the -l or --lastname flags are set, it sets the the last name variable
  • When both the firstname and lastname flags are set, it prints a welcome message and returns without error

In addition to the basic logic, we can see that the code leverages a piece of functionality called getopts. Getopts allows us to grab the program parameter flags for use within our program. There are also primitives, which we have learned as well—conditional logic, while loop, and case/switch statements. Once a script develops into more than a simple utility or provides more than a single function, the more basic Bash constructs will become commonplace.

#!/bin/bash

HELP_STR="usage: $0 [-h] [-f] [-l] [--firstname[=]<value>] [--lastname[=]<value] [--help]"

# Notice hidden variables and other built-in Bash functionality
optspec=":flh-:"
while getopts "$optspec" optchar; do
case "${optchar}" in
-)
case "${OPTARG}" in
firstname)
val="${!OPTIND}"; OPTIND=$(( $OPTIND + 1 ))
FIRSTNAME="${val}"
;;
lastname)
val="${!OPTIND}"; OPTIND=$(( $OPTIND + 1 ))
LASTNAME="${val}"
;;
help)
val="${!OPTIND}"; OPTIND=$(( $OPTIND + 1 ))
;;
*)
if [ "$OPTERR" = 1 ] && [ "${optspec:0:1}" != ":" ]; then
echo "Found an unknown option --${OPTARG}" >&2
fi
;;
esac;;
f)
val="${!OPTIND}"; OPTIND=$(( $OPTIND + 1 ))
FIRSTNAME="${val}"
;;
l)
val="${!OPTIND}"; OPTIND=$(( $OPTIND + 1 ))
LASTNAME="${val}"
;;
h)
echo "${HELP_STR}" >&2
exit 2
;;
*)
if [ "$OPTERR" != 1 ] || [ "${optspec:0:1}" = ":" ]; then
echo "Error parsing short flag: '-${OPTARG}'" >&2
exit 1
fi

;;
esac
done

# Do we have even one argument?
if [ -z "$1" ]; then
echo "${HELP_STR}" >&2
exit 2
fi

# Sanity check for both Firstname and Lastname
if [ -z "${FIRSTNAME}" ] || [ -z "${LASTNAME}" ]; then
echo "Both firstname and lastname are required!"
exit 3
fi

echo "Welcome ${FIRSTNAME} ${LASTNAME}!"

exit 0

When we execute the preceding program, we should expect responses similar to the following:

$ bash flags.sh 
usage: flags.sh [-h] [-f] [-l] [--firstname[=]<value>] [--lastname[=]<value] [--help]
$ bash flags.sh -h
usage: flags.sh [-h] [-f] [-l] [--firstname[=]<value>] [--lastname[=]<value] [--help]
$ bash flags.sh --fname Bob
Both firstname and lastname are required!
rbrash@moon:~$ bash flags.sh --firstname To -l Mater
Welcome To Mater!
主站蜘蛛池模板: 娱乐| 大埔县| 内丘县| 教育| 绥化市| 平阳县| 嘉定区| 兴宁市| 舟山市| 马尔康县| 宁强县| 靖远县| 平利县| 曲周县| 汝阳县| 遂溪县| 南涧| 霍林郭勒市| 长春市| 金溪县| 安乡县| 金堂县| 天柱县| 青河县| 张家口市| 屏南县| 屏山县| 无棣县| 长宁县| 阳新县| 五台县| 静乐县| 定结县| 广南县| 紫云| 阿坝县| 汕尾市| 平和县| 盐山县| 水城县| 图们市|