How to Get The Bash Date Script to Return a Day of The Week Relative to a Non-Current Time

How do I get the bash date script to return a day of the week relative to a non-current time?

You can use a little day number arithmetic:

base="02/1/2012"
feb1_dayofweek=$( date -d $base +%w )
target_dayofweek=0   # sunday
date -d "$base - $(( (7 + feb1_dayofweek - target_dayofweek) % 7 )) days"

result:

Sun Jan 29 00:00:00 EST 2012

Get the date (a day before current time) in Bash

Sorry not mentioning I on Solaris system.
As such, the -date switch is not available on Solaris bash.

I find out I can get the previous date with little trick on timezone.

DATE=`TZ=MYT+16 date +%Y-%m-%d_%r`
echo $DATE

Get Day Of Week in bash script

Use %u. Like this:

DOW=$(date +%u)

From the man page:

%u day of week (1..7); 1 is Monday

How do I get the first day of the given year's day of the week in Bash Shell?

Please see the below code which will give you 1 first day of the year passed:

# !/usr/bin/bash
year=2020
firstday=`date -d "01 Jan $year" +'%A,%d'`
echo "First day of the year '$year' is : '$firstday'"

Output:
First day of the year '2020' is : 'Wednesday,01'
If you want to just get the day , then remove the %d option.

firstday=`date -d "01 Jan $year" +'%A`

Output :First day of the year '2020' is : 'Wednesday'

How to increment datetime by custom months in python without using library

Edit - based on your comment of dates being needed to be rounded down if there are fewer days in the next month, here is a solution:

import datetime
import calendar

def add_months(sourcedate, months):
    month = sourcedate.month - 1 + months
    year = sourcedate.year + month // 12
    month = month % 12 + 1
    day = min(sourcedate.day, calendar.monthrange(year,month)[1])
    return datetime.date(year, month, day)

In use:

>>> somedate = datetime.date.today()
>>> somedate
datetime.date(2010, 11, 9)
>>> add_months(somedate,1)
datetime.date(2010, 12, 9)
>>> add_months(somedate,23)
datetime.date(2012, 10, 9)
>>> otherdate = datetime.date(2010,10,31)
>>> add_months(otherdate,1)
datetime.date(2010, 11, 30)

Also, if you're not worried about hours, minutes and seconds you could use date rather than datetime. If you are worried about hours, minutes and seconds you need to modify my code to use datetime and copy hours, minutes and seconds from the source to the result.

execution_date in airflow: need to access as a variable

The BashOperator's bash_command argument is a template. You can access execution_date in any template as a datetime object using the execution_date variable. In the template, you can use any jinja2 methods to manipulate it.

Using the following as your BashOperator bash_command string:

# pass in the first of the current month
some_command.sh {{ execution_date.replace(day=1) }}

# last day of previous month
some_command.sh {{ execution_date.replace(day=1) - macros.timedelta(days=1) }}

If you just want the string equivalent of the execution date, ds will return a datestamp (YYYY-MM-DD), ds_nodash returns same without dashes (YYYYMMDD), etc. More on macros is available in the Api Docs.

---

Your final operator would look like:

command = """curl -XPOST '%(hostname)s:8000/run?st={{ ds }}'""" % locals()
t1 = BashOperator( task_id='rest-api-1', bash_command=command, dag=dag)

Python - Get Yesterday's date as a string in YYYY-MM-DD format

You Just need to subtract one day from today's date. In Python datetime.timedelta object lets you create specific spans of time as a timedelta object.

datetime.timedelta(1) gives you the duration of "one day" and is subtractable from a datetime object. After you subtracted the objects you can use datetime.strftime in order to convert the result --which is a date object-- to string format based on your format of choice:

>>> from datetime import datetime, timedelta
>>> yesterday = datetime.now() - timedelta(1)

>>> type(yesterday)                                                                                                                                                                                    
>>> datetime.datetime    

>>> datetime.strftime(yesterday, '%Y-%m-%d')
'2015-05-26'

Note that instead of calling the datetime.strftime function, you can also directly use strftime method of datetime objects:

>>> (datetime.now() - timedelta(1)).strftime('%Y-%m-%d')
'2015-05-26'

As a function:

from datetime import datetime, timedelta

def yesterday(frmt='%Y-%m-%d', string=True):
    yesterday = datetime.now() - timedelta(1)
    if string:
        return yesterday.strftime(frmt)
    return yesterday

example:

In [10]: yesterday()
Out[10]: '2022-05-13'

In [11]: yesterday(string=False)
Out[11]: datetime.datetime(2022, 5, 13, 12, 34, 31, 701270)

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