命令列程式是单独存在的执行档，执行前，Shell 会现在 $PATH 中寻找，若有同名但不同路径的档案，先找到先执行
常用的命令列程式：
cp,date,who,w,ls,cat,cut,wc,last,mv,mkdir,rmdir,mv,ps,pgrep,top,df,dd,ln,sort,sed,awk,ifconfig,dmesg, diff,hostname,dnsdomainname,chmod,chown,chgrp,grep,find,kill,killall,pkill,more,less,mount,nice,paste, ping,seq,sleep,su,tar,gzip,xargs,touch,uname,basename,dirname,tr,uniq,mail,which,locate,getconf
- which 由预设的所寻路径 PATH 中，找到命令列程式的档案位置（默认找到第一个）。 -a 找出所有符合的程式路径
- locate 由档案资料库中，找出包含「关键字」的档案路径
凡是档案路径中，含有此关键字的，都会被列出来
- date 展示、设定系统的日期和时间
FORMAT controls the output. Interpreted sequences are: %% a literal % %a locale's abbreviated weekday name (e.g., Sun) %A locale's full weekday name (e.g., Sunday) %b locale's abbreviated month name (e.g., Jan) %B locale's full month name (e.g., January) %c locale's date and time (e.g., Thu Mar 3 23:05:25 2005) %C century; like %Y, except omit last two digits (e.g., 20) %d day of month (e.g., 01) %D date; same as %m/%d/%y %e day of month, space padded; same as %_d %F full date; same as %Y-%m-%d %g last two digits of year of ISO week number (see %G) %G year of ISO week number (see %V); normally useful only with %V %h same as %b %H hour (00..23) %I hour (01..12) %j day of year (001..366) %k hour, space padded ( 0..23); same as %_H %l hour, space padded ( 1..12); same as %_I %m month (01..12) %M minute (00..59) %n a newline %N nanoseconds (000000000..999999999) %p locale's equivalent of either AM or PM; blank if not known %P like %p, but lower case %r locale's 12-hour clock time (e.g., 11:11:04 PM) %R 24-hour hour and minute; same as %H:%M %s seconds since 1970-01-01 00:00:00 UTC %S second (00..60) %t a tab %T time; same as %H:%M:%S %u day of week (1..7); 1 is Monday %U week number of year, with Sunday as first day of week (00..53) %V ISO week number, with Monday as first day of week (01..53) %w day of week (0..6); 0 is Sunday %W week number of year, with Monday as first day of week (00..53) %x locale's date representation (e.g., 12/31/99) %X locale's time representation (e.g., 23:13:48) %y last two digits of year (00..99) %Y year %z +hhmm numeric time zone (e.g., -0400) %:z +hh:mm numeric time zone (e.g., -04:00) %::z +hh:mm:ss numeric time zone (e.g., -04:00:00) %:::z numeric time zone with : to necessary precision (e.g., -04, +05:30) %Z alphabetic time zone abbreviation (e.g., EDT) By default, date pads numeric fields with zeroes. The following optional flags may follow '%': - (hyphen) do not pad the field _ (underscore) pad with spaces 0 (zero) pad with zeros ^ use upper case if possible # use opposite case if possible After any flags comes an optional field width, as a decimal number; then an optional modifier, which is either E to use the locale's alternate representations if available, or O to use the locale's alternate numeric symbols if available. Examples: Convert seconds since the epoch (1970-01-01 UTC) to a date $ date --date='@2147483647' Show the time on the west coast of the US (use tzselect(1) to find TZ) $ TZ='America/Los_Angeles' date Show the local time for 9AM next Friday on the west coast of the US $ date --date='TZ="America/Los_Angeles" 09:00 next Fri'
