bash - 什么是特殊的美元符号shell变量？(What are the special dollar sign shell variables?)

Question

In Bash, there appear to be several variables which hold special, consistently-meaning values.

(在Bash中，似乎有几个变量具有特殊的，一致意义的值。)

For instance,

(例如，)

./myprogram &; echo $!

will return the PID of the process which backgrounded myprogram .

(将返回后面的myprogram进程的PID。)

I know of others, such as $?

(我知道别人，比如$?)

which I think is the current TTY.

(我认为是目前的TTY。)

Are there others?

(还有其他人吗？)

  ask by Z Douglas translate from so

Answer 1

• $1 , $2 , $3 , ... are the positional parameters .

  ($1 ， $2 ， $3 ，...是位置参数 。)

• "$@" is an array-like construct of all positional parameters, {$1, $2, $3 ...} .

  ("$@"是所有位置参数的数组式构造， {$1, $2, $3 ...} 。)

• "$*" is the IFS expansion of all positional parameters, $1 $2 $3 ... .

  ("$*"是所有位置参数的IFS扩展， $1 $2 $3 ...)

• $# is the number of positional parameters.

  ($#是位置参数的数量。)

• $- current options set for the shell.

  ($-为shell设置的当前选项。)

• $$ pid of the current shell (not subshell).

  (当前shell的$$ pid（不是子shell）。)

• $_ most recent parameter (or the abs path of the command to start the current shell immediately after startup).

  ($_最近的参数（或启动后立即启动当前shell的命令的abs路径）。)

• $IFS is the (input) field separator.

  ($IFS是（输入）字段分隔符。)

• $? is the most recent foreground pipeline exit status.

  (是最新的前台管道退出状态。)

• $! is the PID of the most recent background command.

  (是最近的后台命令的PID。)

• $0 is the name of the shell or shell script.

  ($0是shell或shell脚本的名称。)

Most of the above can be found under Special Parameters in the Bash Reference Manual.

(以上大部分内容可以在Bash参考手册中的特殊参数下找到。)

There are all the environment variables set by the shell .

(shell设置了所有环境变量 。)

For a comprehensive index, please see the Reference Manual Variable Index .

(有关综合索引，请参阅参考手册变量索引 。)