file
file功能说明：辨识文件类型。
语 法：file [-beLvz][-f <名称文件>][-m <魔法数字文件>...][文件或目录...]
补充说明：通过file指令，我们得以辨识该文件的类型。
参 数：
-b 列出辨识结果时，不显示文件名称。
-c 详细显示指令执行过程，便于排错或分析程序执行的情形。
-f<名称文件> 指定名称文件，其内容有一个或多个文件名称呢感，让file依序辨识这些文件，格式为每列一个文件名称。
-L 直接显示符号连接所指向的文件的类别。
-m<魔法数字文件> 指定魔法数字文件。
-v 显示版本信息。
-z 尝试去解读压缩文件的内容。
file
file [options] files
Classify the named files according to the type of data they contain. file checks the magic file (usually /usr/share/magic) to identify some file types.
Options
Brief mode; do not prepend filenames to output lines.
Check the format of the magic file (files argument is invalid with -c). Usually used with -m.
Read the names of files to be checked from file.
Follow symbolic links. By default, symbolic links are not followed.
Search for file types in file instead of /usr/share/magic.
Flush standard output after checking a file.
Check files that are block or character special files in addition to checking ordinary files.
Print the version.
Attempt checking of compressed files.
Many file types are understood. Output lists each filename, followed by a brief classification such as:
ascii text c program text c-shell commands data empty iAPX 386 executable directory [nt] roff, tbl, or eqn input text shell commands symbolic link to ../usr/etc/arp
Example
List all files that are deemed to be troff/nroff input:
file * | grep roff