bash 如何检查是否存在第二个参数
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How to check for the existence of a second argument
提问by cade galt
I need to update this bash function I use for doing things with git:
我需要更新我用来处理 git 的这个 bash 函数：
push() {
a=
if [ $# -eq 0 ]
then
a=$(timestamp)
fi
# ... do stuff
}
but I don't know how this line works
但我不知道这条线是如何运作的
if [ $# -eq 0 ]
I need to check for a first argument and then I need to check for a second argument.
我需要检查第一个参数，然后我需要检查第二个参数。
So there will be 2 if statements.
所以会有2个if语句。
How can I update this and how does this line work
我怎样才能更新这个以及这条线是如何工作的
if [ $# -eq 0 ]
采纳答案by joranvar
You could create a small script to look into how $#changes when you call the function with different numbers of arguments. For instance:
您可以创建一个小脚本来查看$#当您使用不同数量的参数调用函数时会发生什么变化。例如：
[Contents of "push.sh":]
[“push.sh”的内容：]
push() {
echo $#
}
echo "First call, no arguments:"
push
echo "Second call, one argument:"
push "First argument"
echo "Third call, two arguments:"
push "First argument" "And another one"
If you put this in a script and run it, you'll see something like:
如果你把它放在一个脚本中并运行它，你会看到类似的东西：
-> % ./push.sh
First call, no arguments:
0
Second call, one argument:
1
Third call, two arguments:
2
This tells you that the value of $#contains the number of arguments given to the function.
这告诉您 的值$#包含提供给函数的参数数量。
The if [ $# -eq 0 ]part you can add to the script, and change the 0 to some other numbers to see what happens. Also, an internet search for "bash if" will reveal the meaning of the -eqpart, and show that you could also use -ltor -gt, for instance, testing whether a number is less than or greater than another.
该if [ $# -eq 0 ]部分可以添加到脚本，将0改为其他一些数字来看看会发生什么。此外，在互联网上搜索“ bash if”将揭示该-eq部分的含义，并表明您还可以使用-ltor -gt，例如，测试一个数字是小于还是大于另一个。
In the end, you'll likely want to use something like the following:
最后，您可能希望使用以下内容：
a=
b=
if [ $# -lt 1 ]
then
a=$(timestamp)
fi
if [ $# -lt 2 ]
then
b=$(second thing)
fi
回答by Lix
The $#part is a variable that contains the number of arguments passed to the script.
该$#部分是一个变量，包含传递给脚本的参数数量。
The conditional statement there checks the value of that variable using -eqand it's checking if the value is zero (as in no arguments were passed).
那里的条件语句使用检查该变量的值，-eq并检查该值是否为零（因为没有传递参数）。
In order to check for two arguments, you can change (or add) that line to read like this:
为了检查两个参数，您可以更改（或添加）该行，如下所示：
if [ $# -eq 2 ]
