GNU date and relatives dates

I was writing a simple script to delete some log files, all the log filenames contain the date of creation in the form YYYYMMDD and I needed to delete the files from previous month keeping the current month. The script will run on the last day of every month.

I thought the task will be very easy as I could use the GNU date command to build the date string, something like:

# The year
date +%Y

Use the date relative option for getting the previous month, something like:

date --date="-1 month" +%m

Then concatenate both strings and build a file pattern using wildcards like ? and *.

The system date was 2019-05-31 ahd I was expecting the 04 string as the output, instead 05 was printed.

I tried several variants and all printed the same, 05:

$ date --date="-1 month" +%m
05

$ date --date="last month" +%m
05

I DuckDuckGoed the Internet and found this answer:

https://stackoverflow.com/questions/13168463/using-date-command-to-get-previous-current-and-next-month

This is from the coreutils manual online:

https://www.gnu.org/software/coreutils/manual/html_node/Relative-items-in-date-strings.html#Relative-items-in-date-strings

$ date --date="$(date +%Y%m15) -1 month" +%m
04

What Week Day Is That Date in the Past?

A solution for: http://www.linuxjournal.com/content/work-shell-what-day-date-past

No AWK involved.


#!/bin/bash


# We need 3 arguments:
# DOW, Month and Day


if [ $# -ne 3 ]
then
        echo "Usage: $(basename $0) weekday month day"
        echo "(example: $(basename $0) 4 3 2)"
        exit 1
fi


# We use the date command for checking


date -d "$2/$3" &> /dev/null


if [ "$?" == "1" ]
then
        echo "$(basename $0) Error: Invalid date!"
        exit 1
fi


# Month as number
M=$(date -d "$2/$3" +%m)


# The day of the month
D=$(date -d "$2/$3" +%e | sed 's/ //')


WD=$1


# The day of year is gonna help us decide which is
# the first year to test: current year or the previous one
DOY=$(date -d "$2/$3" +%j)
CDOY=$(date +%j)


Y=$(date +%Y)


if [ ${DOY} -gt ${CDOY} ]
then
        Y=$(expr ${Y} - 1)
fi


echo $M $D $WD $DOY $CDOY $Y


F=''
until [ -n "${F}" ]
do
        echo -n $Y $M =


        # The calendar for the month and year
        # Extract the line with the day of the month
        # Add numbers to the lines, the number will be
        # used to identify the Day of the Week
        # Extract the line of the particular day
        # gotta be careful cause 6 1 is the sixth line day 1
        # and 1 6 is the first line day 6, so we search by the second number
        # Convert the multiple spaces in front of the numbers into one space
        # so the cut command always return the second field
        # Extract the first number only, that's the DOW


        CWD=$(cal ${M} ${Y} \

                | grep "\b${D}\b" \
                | sed 's/[ ][ ][ ]\|[ ][ ]\|[ ]/|/g; s/^|//; s/|/\n/g' \
                | cat -n \
                | grep "\b${D}\b$" \
                | tr -s [:space:] ' ' \
                | cut -d ' ' -f 2)


        if [ ${WD} -eq ${CWD} ]
        then
                F=Found
        fi


        echo $CWD


        Y=$(expr ${Y} - 1)
done


##END##

The output of searching the first date in the past when March 1 was Wednesday:

janeiros@harlie:~/tmp$ ./t.sh 4 3 1

03 1 4 061 087 2012

2012 03 =5

2011 03 =3

2010 03 =2

2009 03 =1

2008 03 =7

2007 03 =5

2006 03 =4

janeiros@harlie:~/tmp$ cal 3 2006

     March 2006

Su Mo Tu We Th Fr Sa

          1  2  3  4

 5  6  7  8  9 10 11

12 13 14 15 16 17 18

19 20 21 22 23 24 25

26 27 28 29 30 31

Previous date in bash

Sometimes I need the previous date in my scripts:

DATE=$(date +%Y%m%d --date=-1day)

For 10/5/2011 DATE = 20111004

$ date --version
date (GNU coreutils) 6.10

Date formatting in Perl

use Date::Format;
my $Time = time2str("%D", time());

Give something like 07/20/11

Package libtimedate-perl (in hardy, Ubuntu 8.04.3 LTS)

dpkg -S Date::Format

Yesterday in MySQL query

SELECT * FROM table
WHERE date = CURDATE() - INTERVAL 1 DAY;

Playing with DATE and FOR in XP DOS

@echo off

rem for /F "tokens=1-4 delims=/ " %%i in ('date /t') do set dow=%%i && set month=%%j && set day=%%k && set year=%%l

rem for /F "tokens=1-4 delims=/ " %%i in ('date /t') do set dow=%%i && set date=%%j-%%k-%%l

rem for /F "tokens=2-4 delims=/ " %%i in ('date /t') do set date=%%i-%%j-%%k

for /F "tokens=1-4 delims=/ " %%i in ("%DATE%") do (

set dow=%%i

set dom=%%j-%%k-%%l

set month=%%j

set day=%%k

set year=%%l

)

set datew=%DATE:~0,3%

set datem=%DATE:~4,2%-%DATE:~7,2%-%DATE:~10,4%

set daten=%month%.%day%.%year%

echo %dow%

echo %datew%

echo %datem%

echo %daten%