@rob mayoff 的回答是完成此任务的最简单方法，但我想我会尝试将您的伪代码转换为真正的 shell 语法，以指出一些习惯于“真正”编程语言的人的标准陷阱。先说三点一般注意事项：
- 不同的shell 有不同的功能，所以如果您需要任何bash 扩展，请使用bash（即使用命令启动脚本
#!/bin/bash或运行它）。bash如果您只使用基本的 Bourne shell 功能和语法，请改用 sh （#!/bin/sh或sh命令）运行它。如果你不知道，假设你需要 bash。
- 在为以后执行构建命令时，您可能会遇到各种解析异常（请参阅BashFAQ#050：我正在尝试将命令放入变量中，但复杂的情况总是失败！）。最好的方法通常是将其构建为数组，而不是字符串。'当然，数组是 bash 扩展，而不是基本的 shell 功能......
- 在 shell 语法中，空格很重要。例如，在 command
if [ -n "$2" ]; then中，分号后的空格是可选的（分号前也可以有一个空格），但所有其他空格都是必需的（没有它们，命令将执行完全不同的操作）。此外，在作业中，等号周围不能有空格，或者（再次）它会做一些完全不同的事情。
考虑到这一点，这是我对该功能的看法：
addUser() {
# The function keyword is optional and nonstandard, just leave it off. Also,
# shell functions don't declare their arguments, they just parse them later
# as $1, $2, etc
bashCmd=(useradd -m)
# you don't have to declare variable types, just assign to them -- the
# parentheses make this an array. Also, you don't need semicolons at the
# end of a line (only use them if you're putting another command on the
# same line). Also, you don't need quotes around literal strings, because
# everything is a string by default. The only reason you need quotes is to
# prevent/limit unwanted parsing of various shell metacharacters and such.
# Adding the initial user group
if [ -z "$3" ]; then
# [ is actually a command (a synonym for test), so it has some ... parsing
# oddities. The -z operator checks whether a string is empty (zero-length).
# The double-quotes around the string to be tested are required in this case,
# since otherwise if it's zero-length it'll simply vanish. Actually, you
# should almost always have variables in double-quotes to prevent accidental
# extra parsing.
# BTW, since this is a bash script, we could use [[ ]] instead, which has
# somewhat cleaner syntax, but I'm demonstrating the difficult case here.
bashCmd+=(-g users)
else
bashCmd+=(-g "$3")
# Here, double-quotes here are not required, but a good idea in case
# the third argument happens to contain any shell metacharacters --
# double-quotes prevent them from being interpreted here. -g doesn't
# have any shell metacharacters, so putting quotes around it is not
# necessary (but wouldn't be harmful either).
fi
# Adding any additional groups
if [ -n "$4" ]; then
bashCmd+=(-G "$4")
fi
# Set the login shell
if [ -z "$2" ]; then
bashCmd+=(-s /bin/bash "$1")
else
bashCmd+=(-s "$2" "$1")
fi
# Finally, run the command
"${bashCmd[@]}"
# This is the standard idiom for expanding an array, treating each element
# as a shell word.
}