前Linux中帮助一直使用man，但前提是知道这个命令怎么写。
如果遇到想完成某个功能，但具体命令忘了的时候怎么办能。
新发现从来也没用过的apropos, 直接输入apropos [keyword], 即可查看与keyword相关功能的命令。
该命令实际完成的是搜索其它命令的描述信息，将相关命令罗列出来，不一定出现的命令就是想要的，但可以从中帮助回忆到有用的命令。
man apropos 自己看。
用apropos查找和sort相关的命令：
apropos sort
alphasort [scandir] (3) - scan a directory for matching entries bsearch (3) - binary search of a sorted array bsearch (3p) - binary search a sorted table bunzip2 (1) - a block-sorting file compressor, v1.0.2 bunzip2 [bzcat] (1) - a block-sorting file compressor, v1.0.2 bunzip2 [bzip2] (1) - a block-sorting file compressor, v1.0.2 bunzip2 [bzip2recover] (1) - a block-sorting file compressor, v1.0.2 bzip2 (1) - a block-sorting file compressor, v1.0.2 bzip2 [bunzip2] (1) - a block-sorting file compressor, v1.0.2 bzip2 [bzcat] (1) - a block-sorting file compressor, v1.0.2 bzip2 [bzip2recover] (1) - a block-sorting file compressor, v1.0.2 comm (1) - compare two sorted files line by line iterator_info_s [netsnmp_iterator_info_s] (3) - Holds iterator information containing functions which should be called by the iterator_handler to loop over your data set and sort it in a SNMP specific manner ldap_sort_entries (3) - LDAP sorting routines ldap_sort_entries [ldap_sort] (3) - LDAP sorting routines ldap_sort_entries [ldap_sort_strcasecmp] (3) - LDAP sorting routines ldap_sort_entries [ldap_sort_values] (3) - LDAP sorting routines ldap_sort_strcasecmp (3) - LDAP sorting routines ldap_sort_strcasecmp [ldap_sort] (3) - LDAP sorting routines ldap_sort_strcasecmp [ldap_sort_entries] (3) - LDAP sorting routines ldap_sort_strcasecmp [ldap_sort_values] (3) - LDAP sorting routines ldap_sort_values (3) - LDAP sorting routines ldap_sort_values [ldap_sort] (3) - LDAP sorting routines ldap_sort_values [ldap_sort_entries] (3) - LDAP sorting routines ldap_sort_values [ldap_sort_strcasecmp] (3) - LDAP sorting routines lsort (n) - Sort the elements of a list qsort (3) - sorts an array qsort (3p) - sort a table of data sort (1) - sort lines of text files sort (1p) - sort, merge, or sequence check text files sort (3pm) - perl pragma to control sort() behaviour texindex (1) - sort Texinfo index files tsort (1) - perform topological sort tsort (1p) - topological sort uniq (1) - remove duplicate lines from a sorted file versionsort [scandir] (3) - scan a directory for matching entries