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copied!<p>I have written a bash script for converting dates expressed in English into conventional mm/dd/yyyy dates. It is called <strong>ComputeDate</strong>.</p> <p>Here are some examples of its use. For brevity I have placed the output of each invocation on the same line as the invocation, separarted by a colon (:). The quotes shown below are <em>not</em> necessary when running <strong>ComputeDate</strong>:</p> <pre><code>$ ComputeDate 'yesterday': 03/19/2010 $ ComputeDate 'yes': 03/19/2010 $ ComputeDate 'today': 03/20/2010 $ ComputeDate 'tod': 03/20/2010 $ ComputeDate 'now': 03/20/2010 $ ComputeDate 'tomorrow': 03/21/2010 $ ComputeDate 'tom': 03/21/2010 $ ComputeDate '10/29/32': 10/29/2032 $ ComputeDate 'October 29': 10/1/2029 $ ComputeDate 'October 29, 2010': 10/29/2010 $ ComputeDate 'this monday': 'this monday' has passed. Did you mean 'next monday?' $ ComputeDate 'a week after today': 03/27/2010 $ ComputeDate 'this satu': 03/20/2010 $ ComputeDate 'next monday': 03/22/2010 $ ComputeDate 'next thur': 03/25/2010 $ ComputeDate 'mon in 2 weeks': 03/28/2010 $ ComputeDate 'the last day of the month': 03/31/2010 $ ComputeDate 'the last day of feb': 2/28/2010 $ ComputeDate 'the last day of feb 2000': 2/29/2000 $ ComputeDate '1 week from yesterday': 03/26/2010 $ ComputeDate '1 week from today': 03/27/2010 $ ComputeDate '1 week from tomorrow': 03/28/2010 $ ComputeDate '2 weeks from yesterday': 4/2/2010 $ ComputeDate '2 weeks from today': 4/3/2010 $ ComputeDate '2 weeks from tomorrow': 4/4/2010 $ ComputeDate '1 week after the last day of march': 4/7/2010 $ ComputeDate '1 week after next Thursday': 4/1/2010 $ ComputeDate '2 weeks after the last day of march': 4/14/2010 $ ComputeDate '2 weeks after 1 day after the last day of march': 4/15/2010 $ ComputeDate '1 day after the last day of march': 4/1/2010 $ ComputeDate '1 day after 1 day after 1 day after 1 day after today': 03/24/2010 </code></pre> <p>I have included this script as an answer to this problem because it illustrates how to do date arithmetic via a set of bash functions and these functions may prove useful for others. It handles leap years and leap centuries correctly:</p> <pre><code>#! /bin/bash # ConvertDate -- convert a human-readable date to a MM/DD/YY date # # Date ::= Month/Day/Year # | Month/Day # | DayOfWeek # | [this|next] DayOfWeek # | DayofWeek [of|in] [Number|next] weeks[s] # | Number [day|week][s] from Date # | the last day of the month # | the last day of Month # # Month ::= January | February | March | April | May | ... | December # January ::= jan | january | 1 # February ::= feb | january | 2 # ... # December ::= dec | december | 12 # Day ::= 1 | 2 | ... | 31 # DayOfWeek ::= today | Sunday | Monday | Tuesday | ... | Saturday # Sunday ::= sun* # ... # Saturday ::= sat* # # Number ::= Day | a # # Author: Larry Morell if [ $# = 0 ]; then printdirections $0 exit fi # Request the value of a variable GetVar () { Var=$1 echo -n "$Var= [${!Var}]: " local X read X if [ ! -z $X ]; then eval $Var="$X" fi } IsLeapYear () { local Year=$1 if [ $[20$Year % 4] -eq 0 ]; then echo yes else echo no fi } # AddToDate -- compute another date within the same year DayNames=(mon tue wed thu fri sat sun ) # To correspond with 'date' output Day2Int () { ErrorFlag= case $1 in -e ) ErrorFlag=-e; shift ;; esac local dow=$1 n=0 while [ $n -lt 7 -a $dow != "${DayNames[n]}" ]; do let n++ done if [ -z "$ErrorFlag" -a $n -eq 7 ]; then echo Cannot convert $dow to a numeric day of wee exit fi echo $[n+1] } Months=(31 28 31 30 31 30 31 31 30 31 30 31) MonthNames=(jan feb mar apr may jun jul aug sep oct nov dec) # Returns the month (1-12) from a date, or a month name Month2Int () { ErrorFlag= case $1 in -e ) ErrorFlag=-e; shift ;; esac M=$1 Month=${M%%/*} # Remove /... case $Month in [a-z]* ) Month=${Month:0:3} M=0 while [ $M -lt 12 -a ${MonthNames[M]} != $Month ]; do let M++ done let M++ esac if [ -z "$ErrorFlag" -a $M -gt 12 ]; then echo "'$Month' Is not a valid month." exit fi echo $M } # Retrieve month,day,year from a legal date GetMonth() { echo ${1%%/*} } GetDay() { echo $1 | col / 2 } GetYear() { echo ${1##*/} } AddToDate() { local Date=$1 local days=$2 local Month=`GetMonth $Date` local Day=`echo $Date | col / 2` # Day of Date local Year=`echo $Date | col / 3` # Year of Date local LeapYear=`IsLeapYear $Year` if [ $LeapYear = "yes" ]; then let Months[1]++ fi Day=$[Day+days] while [ $Day -gt ${Months[$Month-1]} ]; do Day=$[Day - ${Months[$Month-1]}] let Month++ done echo "$Month/$Day/$Year" } # Convert a date to normal form NormalizeDate () { Date=`echo "$*" | sed 'sX *X/Xg'` local Day=`date +%d` local Month=`date +%m` local Year=`date +%Y` #echo Normalizing Date=$Date > /dev/tty case $Date in */*/* ) Month=`echo $Date | col / 1 ` Month=`Month2Int $Month` Day=`echo $Date | col / 2` Year=`echo $Date | col / 3` ;; */* ) Month=`echo $Date | col / 1 ` Month=`Month2Int $Month` Day=1 Year=`echo $Date | col / 2 ` ;; [a-z]* ) # Better be a month or day of week Exp=${Date:0:3} case $Exp in jan|feb|mar|apr|may|june|jul|aug|sep|oct|nov|dec ) Month=$Exp Month=`Month2Int $Month` Day=1 #Year stays the same ;; mon|tue|wed|thu|fri|sat|sun ) # Compute the next such day local DayOfWeek=`date +%u` D=`Day2Int $Exp` if [ $DayOfWeek -le $D ]; then Date=`AddToDate $Month/$Day/$Year $[D-DayOfWeek]` else Date=`AddToDate $Month/$Day/$Year $[7+D-DayOfWeek]` fi # Reset Month/Day/Year Month=`echo $Date | col / 1 ` Day=`echo $Date | col / 2` Year=`echo $Date | col / 3` ;; * ) echo "$Exp is not a valid month or day" exit ;; esac ;; * ) echo "$Date is not a valid date" exit ;; esac case $Day in [0-9]* );; # Day must be numeric * ) echo "$Date is not a valid date" exit ;; esac [0-9][0-9][0-9][0-9] );; # Year must be 4 digits [0-9][0-9] ) Year=20$Year ;; esac Date=$Month/$Day/$Year echo $Date } # NormalizeDate jan # NormalizeDate january # NormalizeDate jan 2009 # NormalizeDate jan 22 1983 # NormalizeDate 1/22 # NormalizeDate 1 22 # NormalizeDate sat # NormalizeDate sun # NormalizeDate mon ComputeExtension () { local Date=$1; shift local Month=`GetMonth $Date` local Day=`echo $Date | col / 2` local Year=`echo $Date | col / 3` local ExtensionExp="$*" case $ExtensionExp in *w*d* ) # like 5 weeks 3 days or even 5w2d ExtensionExp=`echo $ExtensionExp | sed 's/[a-z]/ /g'` weeks=`echo $ExtensionExp | col 1` days=`echo $ExtensionExp | col 2` days=$[7*weeks+days] Due=`AddToDate $Month/$Day/$Year $days` ;; *d ) # Like 5 days or 5d ExtensionExp=`echo $ExtensionExp | sed 's/[a-z]/ /g'` days=$ExtensionExp Due=`AddToDate $Month/$Day/$Year $days` ;; * ) Due=$ExtensionExp ;; esac echo $Due } # Pop -- remove the first element from an array and shift left Pop () { Var=$1 eval "unset $Var[0]" eval "$Var=(\${$Var[*]})" } ComputeDate () { local Date=`NormalizeDate $1`; shift local Expression=`echo $* | sed 's/^ *a /1 /;s/,/ /' | tr A-Z a-z ` local Exp=(`echo $Expression `) local Token=$Exp # first one local Ans= #echo "Computing date for ${Exp[*]}" > /dev/tty case $Token in */* ) # Regular date M=`GetMonth $Token` D=`GetDay $Token` Y=`GetYear $Token` if [ -z "$Y" ]; then Y=$Year elif [ ${#Y} -eq 2 ]; then Y=20$Y fi Ans="$M/$D/$Y" ;; yes* ) Ans=`AddToDate $Date -1` ;; tod*|now ) Ans=$Date ;; tom* ) Ans=`AddToDate $Date 1` ;; the ) case $Expression in *day*after* ) #the day after Date Pop Exp; # Skip the Pop Exp; # Skip day Pop Exp; # Skip after #echo Calling ComputeDate $Date ${Exp[*]} > /dev/tty Date=`ComputeDate $Date ${Exp[*]}` #Recursive call #echo "New date is " $Date > /dev/tty Ans=`AddToDate $Date 1` ;; *last*day*of*th*month|*end*of*th*month ) M=`date +%m` Day=${Months[M-1]} if [ $M -eq 2 -a `IsLeapYear $Year` = yes ]; then let Day++ fi Ans=$Month/$Day/$Year ;; *last*day*of* ) D=${Expression##*of } D=`NormalizeDate $D` M=`GetMonth $D` Y=`GetYear $D` # echo M is $M > /dev/tty Day=${Months[M-1]} if [ $M -eq 2 -a `IsLeapYear $Y` = yes ]; then let Day++ fi Ans=$[M]/$Day/$Y ;; * ) echo "Unknown expression: " $Expression exit ;; esac ;; next* ) # next DayOfWeek Pop Exp dow=`Day2Int $DayOfWeek` # First 3 chars tdow=`Day2Int ${Exp:0:3}` # First 3 chars n=$[7-dow+tdow] Ans=`AddToDate $Date $n` ;; this* ) Pop Exp dow=`Day2Int $DayOfWeek` tdow=`Day2Int ${Exp:0:3}` # First 3 chars if [ $dow -gt $tdow ]; then echo "'this $Exp' has passed. Did you mean 'next $Exp?'" exit fi n=$[tdow-dow] Ans=`AddToDate $Date $n` ;; [a-z]* ) # DayOfWeek ... M=${Exp:0:3} case $M in jan|feb|mar|apr|may|june|jul|aug|sep|oct|nov|dec ) ND=`NormalizeDate ${Exp[*]}` Ans=$ND ;; mon|tue|wed|thu|fri|sat|sun ) dow=`Day2Int $DayOfWeek` Ans=`NormalizeDate $Exp` if [ ${#Exp[*]} -gt 1 ]; then # Just a DayOfWeek #tdow=`GetDay $Exp` # First 3 chars #if [ $dow -gt $tdow ]; then #echo "'this $Exp' has passed. Did you mean 'next $Exp'?" #exit #fi #n=$[tdow-dow] #else # DayOfWeek in a future week Pop Exp # toss monday Pop Exp # toss in/off if [ $Exp = next ]; then Exp=2 fi n=$[7*(Exp-1)] # number of weeks n=$[n+7-dow+tdow] Ans=`AddToDate $Date $n` fi ;; esac ;; [0-9]* ) # Number weeks [from|after] Date n=$Exp Pop Exp; case $Exp in w* ) let n=7*n;; esac Pop Exp; Pop Exp #echo Calling ComputeDate $Date ${Exp[*]} > /dev/tty Date=`ComputeDate $Date ${Exp[*]}` #Recursive call #echo "New date is " $Date > /dev/tty Ans=`AddToDate $Date $n` ;; esac echo $Ans } Year=`date +%Y` Month=`date +%m` Day=`date +%d` DayOfWeek=`date +%a |tr A-Z a-z` Date="$Month/$Day/$Year" ComputeDate $Date $* </code></pre> <p>This script makes extensive use of another script I wrote (called <strong>col</strong> ... many apologies to those who use the standard <strong>col</strong> supplied with Linux). This version of <strong>col</strong> simplifies extracting columns from the stdin. Thus,</p> <pre><code>$ echo a b c d e | col 5 3 2 </code></pre> <p>prints</p> <pre><code>e c b </code></pre> <p>Here it the <strong>col</strong> script:</p> <pre><code>#!/bin/sh # col -- extract columns from a file # Usage: # col [-r] [c] col-1 col-2 ... # where [c] if supplied defines the field separator # where each col-i represents a column interpreted according to the presence of -r as follows: # -r present : counting starts from the right end of the line # -r absent : counting starts from the left side of the line Separator=" " Reverse=false case "$1" in -r ) Reverse=true; shift; ;; [0-9]* ) ;; * )Separator="$1"; shift; ;; esac case "$1" in -r ) Reverse=true; shift; ;; [0-9]* ) ;; * )Separator="$1"; shift; ;; esac # Replace each col-i with $i Cols="" for f in $* do if [ $Reverse = true ]; then Cols="$Cols \$(NF-$f+1)," else Cols="$Cols \$$f," fi done Cols=`echo "$Cols" | sed 's/,$//'` #echo "Using column specifications of $Cols" awk -F "$Separator" "{print $Cols}" </code></pre> <p>It also uses <strong>printdirections</strong> for printing out directions when the script is invoked improperly:</p> <pre><code>#!/bin/sh # # printdirections -- print header lines of a shell script # # Usage: # printdirections path # where # path is a *full* path to the shell script in question # beginning with '/' # # To use printdirections, you must include (as comments at the top # of your shell script) documentation for running the shell script. if [ $# -eq 0 -o "$*" = "-h" ]; then printdirections $0 exit fi # Delete the command invocation at the top of the file, if any # Delete from the place where printdirections occurs to the end of the file # Remove the # comments # There is a bizarre oddity here. sed '/#!/d;/.*printdirections/,$d;/ *#/!d;s/# //;s/#//' $1 > /tmp/printdirections.$$ # Count the number of lines numlines=`wc -l /tmp/printdirections.$$ | awk '{print $1}'` # Remove the last line numlines=`expr $numlines - 1` head -n $numlines /tmp/printdirections.$$ rm /tmp/printdirections.$$ </code></pre> <p>To use this place the three scripts in the files <strong>ComputeDate</strong>, <strong>col</strong>, and <strong>printdirections</strong>, respectively. Place the file in directory named by your PATH, typically, ~/bin. Then make them executable with:</p> <pre><code>$ chmod a+x ComputeDate col printdirections </code></pre> <p>Problems? Send me some emaiL: morell AT cs.atu.edu Place <strong>ComputeDate</strong> in the subject.</p>

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