Bash 手册页显示:“命令替换可以让你用一个命令的输出替换为命令的名字。”这可能不太好理解。 命令替换有两种格式:`command`和$(command)。在更早的格式中使用反引号(`),在命令中使用反斜杠(\)来保持它转义之前的文本含义。然而,当用在新版本的括号格式中时,反斜杠被当做一个特殊字符处理。也请注意带括号的...
/bin/bashCOMMAND="ls"bash-c$COMMAND The command above will list all the directories and files in the current working directory of the script file. We can use the command substitution method to run the command stored in a variable as:
$ cat show-datetime.sh #!/bin/bash cmd="date" if [[ -n "$1" ]] then cmd+=" --date $1" fi # run command stored in cmd variableCopy The idea is that, by default, we’ll show the current date and time. However, if the user provides a specific date as an argument to the...
Variable=$(command) You can also add additional text to support the command output as shown here: Variable="Optional text $(command)" Let me give you a simple example. Here, I have used the whoami command to find the currently logged-in user with the echo command: echo "The current use...
在GNU bash 在线帮助手册的 “3.7.1 Simple Command Expansion” 小节里面有如下说明: When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right. The words that the parser has marked as variable assignments (those preceding the co...
Number of command-line arguments. 传递给脚本或函数的参数个数。 $_ The underscore variable is set at shell startup and contains the absolute file name of the shell or script being executed as passed in the argument list. Subsequently, it expands to the last argument to the previous command,...
Note:There should not be any space around “=” sign in variable assignment. When you use VAR=VALUE, shell sees the “=” as a symbol and treats the command as a variable assignment. When you use VAR = VALUE, shell assumes that VAR must be the name of a command and tries to execut...
<variable-name>=$(command) Here’s an example has been done which save the hostname command output in a variable using the syntax given above: #!/bin/bash # Assign the output of the 'hostname' command to the 'find_hostname' variable find_hostname=$(hostname) # Print the value of ...
To see the exit status at the command prompt, echo the value “$?” A value of 0 means the expression evaluated as true, and a value of 1 means the expression evaluated as false. 变量具有各种类型属性,文件也有各种类型属性 ...
You can use the command line argument with the command as the argument in the command substitution. Example#8: Create a bash file namedcmdsub3.shwith the following script. `basename` command is used here to retrieve the filename from the 2ndcommand line argument and stored in the variable,...