我知道这是一篇较老的文章，但我今天在编写一个脚本时偶然发现了它，该脚本将从日志文件中获取日期和时间并计算delta。下面的脚本当然是多余的，我强烈建议检查我的逻辑和数学。

#!/bin/bash

dTime=""
tmp=""

#firstEntry="$(head -n 1 "$LOG" | sed 's/.*] \([0-9: -]\+\).*/\1/')"
firstEntry="2013-01-16 01:56:37"
#lastEntry="$(tac "$LOG" | head -n 1 | sed 's/.*] \([0-9: -]\+\).*/\1/')"
lastEntry="2014-09-17 18:24:02"

# I like to make the variables easier to parse
firstEntry="${firstEntry//-/ }"
lastEntry="${lastEntry//-/ }"
firstEntry="${firstEntry//:/ }"
lastEntry="${lastEntry//:/ }"

# remove the following lines in production
echo "$lastEntry"
echo "$firstEntry"

# compute days in last entry
for i in `seq 1 $(echo $lastEntry|awk '{print $2}')`; do {
  case "$i" in
   1|3|5|7|8|10|12 )
    dTime=$(($dTime+31))
    ;;
   4|6|9|11 )
    dTime=$(($dTime+30))
    ;;
   2 )
    dTime=$(($dTime+28))
    ;;
  esac
} done

# do leap year calculations for all years between first and last entry
for i in `seq $(echo $firstEntry|awk '{print $1}') $(echo $lastEntry|awk '{print $1}')`; do {
  if [ $(($i%4)) -eq 0 ] && [ $(($i%100)) -eq 0 ] && [ $(($i%400)) -eq 0 ]; then {
    if [ "$i" = "$(echo $firstEntry|awk '{print $1}')" ] && [ $(echo $firstEntry|awk '{print $2}') -lt 2 ]; then {
      dTime=$(($dTime+1))
    } elif [ $(echo $firstEntry|awk '{print $2}') -eq 2 ] && [ $(echo $firstEntry|awk '{print $3}') -lt 29 ]; then {
      dTime=$(($dTime+1))
    } fi
  } elif [ $(($i%4)) -eq 0 ] && [ $(($i%100)) -ne 0 ]; then {
    if [ "$i" = "$(echo $lastEntry|awk '{print $1}')" ] && [ $(echo $lastEntry|awk '{print $2}') -gt 2 ]; then {
      dTime=$(($dTime+1))
    } elif [ $(echo $lastEntry|awk '{print $2}') -eq 2 ] && [ $(echo $lastEntry|awk '{print $3}') -ne 29 ]; then {
      dTime=$(($dTime+1))
    } fi
  } fi
} done

# substract days in first entry
for i in `seq 1 $(echo $firstEntry|awk '{print $2}')`; do {
  case "$i" in
   1|3|5|7|8|10|12 )
    dTime=$(($dTime-31))
    ;;
   4|6|9|11 )
    dTime=$(($dTime-30))
    ;;
   2 )
    dTime=$(($dTime-28))
    ;;
  esac
} done

dTime=$(($dTime+$(echo $lastEntry|awk '{print $3}')-$(echo $firstEntry|awk '{print $3}')))

# The above gives number of days for sample. Now we need hours, minutes, and seconds
# As a bit of hackery I just put the stuff in the best order for use in a for loop
dTime="$(($(echo $lastEntry|awk '{print $6}')-$(echo $firstEntry|awk '{print $6}'))) $(($(echo $lastEntry|awk '{print $5}')-$(echo $firstEntry|awk '{print $5}'))) $(($(echo $lastEntry|awk '{print $4}')-$(echo $firstEntry|awk '{print $4}'))) $dTime"
tmp=1
for i in $dTime; do {
  if [ $i -lt 0 ]; then {
    case "$tmp" in
     1 )
      tmp="$(($(echo $dTime|awk '{print $1}')+60)) $(($(echo $dTime|awk '{print $2}')-1))"
      dTime="$tmp $(echo $dTime|awk '{print $3" "$4}')"
      tmp=1
      ;;
     2 )
      tmp="$(($(echo $dTime|awk '{print $2}')+60)) $(($(echo $dTime|awk '{print $3}')-1))"
      dTime="$(echo $dTime|awk '{print $1}') $tmp $(echo $dTime|awk '{print $4}')"
      tmp=2
      ;;
     3 )
      tmp="$(($(echo $dTime|awk '{print $3}')+24)) $(($(echo $dTime|awk '{print $4}')-1))"
      dTime="$(echo $dTime|awk '{print $1" "$2}') $tmp"
      tmp=3
      ;;
    esac
  } fi
  tmp=$(($tmp+1))
} done

echo "The sample time is $(echo $dTime|awk '{print $4}') days, $(echo $dTime|awk '{print $3}') hours, $(echo $dTime|awk '{print $2}') minutes, and $(echo $dTime|awk '{print $1}') seconds."

您将得到如下输出。

2012 10 16 01 56 37
2014 09 17 18 24 02
The sample time is 700 days, 16 hours, 27 minutes, and 25 seconds.

我修改了一点脚本，使其独立(即。只是设置变量值)，但也许总体思想也是如此。您可能需要对负值进行额外的错误检查。

如果你已经计算出了时间差值，并且它们小于1天，这里有一个非常边缘的BC用例，可以将输出格式化为

HH MM SS.xxxx

24小时格式，请记住小数点右边的数字是以60为基数打印的

Jot -w 'obase = 60;%。3f' - 1.3219567 300 73.6543211 | BC

       01.19 19
    01 14.58 33
    02 28.37 51
    03 42.17 06  # 3 mins 42 secs 
    04 55.56 20  
          ...
          ...
 19 38 10.54 32  # 19 hrs 38 mins 10 secs 
                 #
                 # (or 7:38pm, if it's representing absolute time)

但这绝对是一个快速得到大致数字的方法

这里有一些魔法:

time1=14:30
time2=$( date +%H:%M ) # 16:00
diff=$(  echo "$time2 - $time1"  | sed 's%:%+(1/60)*%g' | bc -l )
echo $diff hours
# outputs 1.5 hours

Sed将a:替换为要转换为1/60的公式。然后用bc计算时间

截至目前(GNU coreutils) 7.4，你现在可以使用-d来做算术:

$ date -d -30days
Sat Jun 28 13:36:35 UTC 2014

$ date -d tomorrow
Tue Jul 29 13:40:55 UTC 2014

你可以使用的单位是天、年、月、小时、分钟和秒:

$ date -d tomorrow+2days-10minutes
Thu Jul 31 13:33:02 UTC 2014

GNU单位:

$ units
2411 units, 71 prefixes, 33 nonlinear units
You have: (10hr+36min+10s)-(10hr+33min+56s)
You want: s
    * 134
    / 0.0074626866
You have: (10hr+36min+10s)-(10hr+33min+56s)
You want: min
    * 2.2333333
    / 0.44776119

#!/bin/bash

START_TIME=$(date +%s)

sleep 4

echo "Total time elapsed: $(date -ud "@$(($(date +%s) - $START_TIME))" +%T) (HH:MM:SS)"

$ ./total_time_elapsed.sh 
Total time elapsed: 00:00:04 (HH:MM:SS)