When authoring tasks configurations, it is often useful to have a set of predefined common variables. VS Code supports variable substitution inside strings in the tasks.json file and has the following predefined variables:

• ${workspaceFolder} the path of the workspace folder that contains the tasks.json file
• ${workspaceRootFolderName} the name of the folder opened in VS Code without any slashes (/)
• ${file} the current opened file
• ${relativeFile} the current opened file relative to the workspace folder containing the file
• ${fileBasename} the current opened file's basename
• ${fileBasenameNoExtension} the current opened file's basename without the extension
• ${fileDirname} the current opened file's dirname
• ${fileExtname} the current opened file's extension
• ${cwd} the task runner's current working directory on startup
• ${lineNumber} the current selected line number in the active file

You can also reference environment variables through ${env:Name} (for example, ${env:PATH}). Be sure to match the environment variable name's casing, for example ${env:Path} on Windows.

Below is an example of a custom task configuration that passes the current opened file to the TypeScript compiler.

{
    "taskName": "TypeScript compile",
    "type": "shell",
    "command": "tsc ${file}",
    "problemMatcher": [
        "$tsc"
    ]

}

部分翻译：（来自互联网）

${workspaceRoot} 当前打开的文件夹的绝对路径+文件夹的名字

            ${workspaceRootFolderName}   当前打开的文件夹的名字

    ${file}当前打开正在编辑的文件名，包括绝对路径，文件名，文件后缀名

${relativeFile}从当前打开的文件夹到当前打开的文件的路径 

如 当前打开的是test文件夹，当前的打开的是main.c，并有test / first / second / main.c

那么此变量代表的是  first / second / main.c

${fileBasename}  当前打开的文件名+后缀名，不包括路径

${fileBasenameNoExtension} 当前打开的文件的文件名，不包括路径和后缀名

${fileDirname} 当前打开的文件所在的绝对路径，不包括文件名

${fileExtname} 当前打开的文件的后缀名

${cwd} the task runner's current working directory on startup

不知道怎么描述，这是原文解释，

跟 cmd 里面的 cwd 是一样的

${lineNumber}  当前打开的文件，光标所在的行数

更新一个链接：https://code.visualstudio.com/docs/editor/variables-reference