Bash、无参数警告和案例决定
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Bash, no-arguments warning, and case decisions
提问by Open the way
I am learning bash.
我正在学习 bash。
I would like to do a simple script that, when not arguments given, shows some message. And when I give numers as argument,s depending on the value, it does one thing or another.
我想做一个简单的脚本，当没有给出参数时，会显示一些消息。当我根据值给出数字作为参数时，它会做一件事或另一件事。
I would also like to know suggestions for the best online manuals for beginners in bash
我还想知道有关 bash 初学者的最佳在线手册的建议
Thanks
谢谢
回答by Thomas
if [[ $# -eq 0 ]] ; then
echo 'some message'
exit 0
fi
case "" in
1) echo 'you gave 1' ;;
*) echo 'you gave something else' ;;
esac
The Advanced Bash-Scripting Guideis pretty good. In spite of its name, it does treat the basics.
该高级Bash脚本编程指南是相当不错的。尽管它的名字，它确实处理基础知识。
回答by Pat
If only interested in bailing if a particular argument is missing, Parameter Substitutionis great:
如果只对缺少特定参数的情况感兴趣，则参数替换很棒：
#!/bin/bash
# usage-message.sh
: ${1?"Usage: if [ -z "$*" ]; then echo "No args"; fi
ARGUMENT"}
# Script exits here if command-line parameter absent,
#+ with following error message.
# usage-message.sh: 1: Usage: usage-message.sh ARGUMENT
回答by Trampas Kirk
Example
例子
No args
Result
结果
if [[ == "" ]] #Where "" is the positional argument you want to validate
then
echo "something"
exit 0
fi
Details
细节
-zis the unary operator for length of string is zero.
$*is all arguments.
The quotes are for safety and encapsulating multiple arguments if present.
-z是字符串长度为零的一元运算符。
$*都是论据。引号是为了安全和封装多个参数（如果存在）。
Use man bashand search (/key) for "unary" for more operators like this.
使用man bash和搜索（/键）“一元”以获得更多这样的运算符。
回答by Ryan Smith
Old but I have reason to rework the answer now thanks to some previous confusion:
旧的，但由于之前的一些混淆，我现在有理由重新编写答案：
##代码##This will echo "Something" if there is no positional argument $1. It does not validate that $1 contains specific information however.
如果没有位置参数 $1，这将回显“Something”。但是，它不会验证 $1 是否包含特定信息。
