readlink是Linux系统中一个常用工具，主要用来找出符号链接所指向的位置。
$readlink --help
Usage: readlink [OPTION]... FILE...
Print value of a symbolic link or canonical file name
-f, --canonicalize canonicalize by following every symlink in
every component of the given name recursively;
all but the last component must exist
-e, --canonicalize-existing canonicalize by following every symlink in
every component of the given name recursively,
all components must exist
-m, --canonicalize-missing canonicalize by following every symlink in
every component of the given name recursively,
without requirements on components existence
-n, --no-newline do not output the trailing delimiter
-q, --quiet,
-s, --silent suppress most error messages
-v, --verbose report error messages
-z, --zero separate output with NUL rather than newline
--help display this help and exit
--version output version information and exit
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report readlink translation bugs to <http://translationproject.org/team/>
For complete documentation, run: info coreutils 'readlink invocation'
举例：系统中的awk命令到底是执行哪个可执行文件呢？
$ readlink /usr/bin/awk
/etc/alternatives/awk ----> 其实这个还是一个符号连接
$ readlink /etc/alternatives/awk
/usr/bin/gawk ----> 这个才是真正的可执行文件
-f： 可以递归跟随给出文件名的所有符号链接以标准化，除最后一个外所有组件必须存在。简单地说，就是一直跟随符号链接，直到非符号链接的文件位置，限制是最后必须存在一个非符号链接的文件。
$ readlink -f /usr/bin/awk
/usr/bin/gawk
ref: https://blog.csdn.net/youmatterhsp/article/details/80375260
