16.3. Time / Date Commands 笔记

Time/date and timing

date

Simply invoked,dateprints the date and time tostdout. Where this command gets interesting is in its formatting and parsing options.
说白了就是一个显示： 日期+时间 的命令

#!/bin/bash
# Exercising the 'date' command

echo "The number of days since the year's beginning is `date +%j`."
# Needs a leading '+' to invoke formatting.
# %j gives day of year.

echo "The number of seconds elapsed since 01/01/1970 is `date +%s`."
#  %s yields number of seconds since "UNIX epoch" began,
#+ but how is this useful?

prefix=temp
suffix=$(date +%s) # The "+%s" option to 'date' is GNU-specific.
filename=$prefix.$suffix
echo "Temporary filename = $filename"
#  It's great for creating "unique and random" temp filenames,
#+ even better than using $$.   这个方法可以生成临时文件，比$$ 的方法好

# Read the 'date

#!/bin/bash
# date-calc.sh
# Author: Nathan Coulter
# Used in ABS Guide with permission (

MPHR=60    # Minutes per hour.
HPD=24     # Hours per day.

diff () {
        printf '%s' $(( $(date -u -d"$TARGET" +%s) -
                        $(date -u -d"$CURRENT" +%s)))
#                       %d = day of month.
} # 两个具体的日期之间相差多少秒


CURRENT=$(date -u -d '2007-09-01 17:30:24' '+%F %T.%N %Z')
TARGET=$(date -u -d'2007-12-25 12:30:00' '+%F %T.%N %Z')
# %F = full date, %T = %H:%M:%S, %N = nanoseconds, %Z = time zone.
# %F= 年-月-日     %T: 小时：分钟：秒    %Z：时区
printf '\nIn 2007, %s ' \
       "$(date -d"$CURRENT +
        $(( $(diff) /$MPHR /$MPHR /$HPD / 2 )) days" '+%d %B')"
#       %B = name of month                ^ halfway      -- eg. %b:1月 %B:一月
printf 'was halfway between %s ' "$(date -d"$CURRENT" '+%d %B')"
printf 'and %s\n' "$(date -d"$TARGET" '+%d %B')"

printf '\nOn %s at %s, there were\n' \
        $(date -u -d"$CURRENT" +%F) $(date -u -d"$CURRENT" +%T)
DAYS=$(( $(diff) / $MPHR / $MPHR / $HPD ))
CURRENT=$(date -d"$CURRENT +$DAYS days" '+%F %T.%N %Z')
HOURS=$(( $(diff) / $MPHR / $MPHR ))
CURRENT=$(date -d"$CURRENT +$HOURS hours" '+%F %T.%N %Z')
MINUTES=$(( $(diff) / $MPHR ))
CURRENT=$(date -d"$CURRENT +$MINUTES minutes" '+%F %T.%N %Z')
printf '%s days, %s hours, ' "$DAYS" "$HOURS"
printf '%s minutes, and %s seconds ' "$MINUTES" "$(diff)"
printf 'until Christmas Dinner!\n\n'

#  Exercise:
# --------
#  Rewrite the diff () function to accept passed parameters,
#+ rather than using global variables.

The date command has quite a number of output options. For example %N gives the nanosecond portion of the current time. One interesting use for this is to generate random integers.

date +%N | sed -e 's/000$//' -e 's/^0//'
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#  Strip off leading and trailing zeroes, if present.
# Length of generated integer depends on
#+ how many zeroes stripped off.

# 115281032
# 63408725
# 394504284

date +%j
# Echoes day of the year (days elapsed since January 1).

date +%k%M
# Echoes hour and minute in 24-hour format, as a single digit string.



# The 'TZ' parameter permits overriding the default time zone.
date                 # Mon Mar 28 21:42:16 MST 2005
TZ=EST date          # Mon Mar 28 23:42:16 EST 2005
# Thanks, Frank Kannemann and Pete Sjoberg, for the tip.


SixDaysAgo=$(date --date='6 days ago')
OneMonthAgo=$(date --date='1 month ago') # Four weeks back (not a
OneYearAgo=$(date --date='1 year ago')

Please Man date for more information!

zdump

    Time zone dump: echoes the time in a specified time zone.

    bash$ zdump EST
    EST  Tue Sep 18 22:09:22 2001 EST


time

    Outputs verbose timing statistics for executing a command.

    time ls -l / gives something like this:

    real    0m0.067s
     user    0m0.004s
     sys     0m0.005s