Linux command note



expr

expr argumentoperator argument

 

1.数学运算器

#expr 30 / 3

10

2.增量计数

$LOOP=0

$LOOP=`expr $LOOP + 1`

*expr表达式加号左右都必须有空格

3.数值测试

如果试图计算非整数，将返回错误

#rr=1.1

#expr $rr + 1

        expr: non-numeric argument

echo

      #echo $?

      返回上一个命令执行结果，如果上一个命令执行正常返回0，不正常返回非0数值

date的日期格式

     

%%  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  dayof 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   anewline

 %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   atab

 %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)