In #!/bin/bash. Unix command to get date of the first of a weekday in a month

Question

I'm looking for a straight Unix commands to get first Sunday of next month, first Monday of next month, first Tuesday of next month, first Wednesday of next month etc.

1. I will need them in the complete date format ( time is not mandatory )

2. I can get numbers like 2, 3, 4 etc. As I don't want only numbers, I will need them in date format (includes day, month, year)

   $ NEXT_MONTH=`date +'%m %Y' -d 'next month'`
   $ echo $NEXT_MONTH
   04 2017
   
   $ NEXT_SUNDAY=`cal $NEXT_MONTH | awk 'NF==7 && !/^Su/{print $1;exit}'`
   $ echo $NEXT_SUNDAY
   2
   

3. I will need these dates to send notifications for the email group.

Ex: I could get the first Saturday of next month as below.

$ firstofmonth=$(date -d '+1 months' '+%Y%m01')
20170401

$ firstsaturday=$(date -d "$firstofmonth" '+%Y-%m')-$((7 - \
                $(date -d "$firstofmonth" '+%u')     ))    
2017-04-1

Answer 1

In ksh93:

$ printf '%(%F)T\n' 'next month, first Monday'
2017-04-03

bash, since 4.2 now supports a %(<format>)T in its printf buitin, but not the ability to parse this kind of date expression.

If you had to use bash and wanted to use that %(<format>)T, you could still do it without forking with something like:

printf -v code '%(
  t=$((%s + (12 - %-H) * 60 * 60))
  increment=$((8 - %u))
  current_month=%m)T' -1
eval "$code"
until
  t=$((t + increment * 24 * 60 * 60)) # next Monday around mid-day
  printf -v code '%(date=%F month=%m)T' "$t"
  eval "$code"
  [ "$month" != "$current_month" ] # until be get to next month
do
  increment=7 # the first increment is the number of days
              # til Monday. Next increments are just a week.
done
echo "$date"

Answer 2

Assuming GNU date (for that -d you're using yourself), and a zsh-like shell for {1..7}:

$ for i in {1..7} ; do \
    LC_ALL=C date '+%Y-%m-%d %a' -d "$(date +%Y%m0${i}) next month" ; \
  done | awk '/Mon/ {print $1}'
2017-04-03

Replace the awk Mon with whatever weekday is required (use LC_ALL=C to get English month names regardless of the user's locale). Also, might be better to store this into a variable if you will be re-querying for each day of the week:

$ days=$(for i in {1..7} ; do \
           LC_ALL=C date '+%Y-%m-%d %a' -d "$(date +%Y%m0${i}) next month" ; \
         done)

$ for i in Mon Tue Wed Thu Fri Sat Sun ; do \
    echo "${days}" | awk "/${i}/"'{print $1}' ; \
  done
2017-04-03
2017-04-04
2017-04-05
2017-04-06
2017-04-07
2017-04-01
2017-04-02

Answer 3

PHP actually makes it pretty easy to parse dates with textual input, if it's available on your system.

Example:

bash-[522]$ php -qr 'date_default_timezone_set("UTC"); echo date("d-m-Y\n", strtotime("first monday of next month"));'
03-04-2017

I have this function in my .bashrc:

get_date ()
{
    text="$*";
    php -qr "date_default_timezone_set(\"UTC\"); echo date(\"d-m-Y\n\", strtotime(\"$text\"));"
}

Which I can use as:

bash-[523]$ get_date first monday of next month
03-04-2017

---

Edit Adding option to use cal

Almost every system that has bash will have cal. The calendar program. You can get a list of the date for the first of each week day by running a combination of cal, date, and awk, as follows:

 cal -hN $(date -d 'next month' +%b' '%Y) | grep -v $(date -d 'next month' +%b) | awk -v date=$(date -d 'next month' +%Y-%m-) '{ printf "%s: "date"%02i\n", $1, $2; }'

Which will give you the following output:

Su: 2017-04-02
Mo: 2017-04-03
Tu: 2017-04-04
We: 2017-04-05
Th: 2017-04-06
Fr: 2017-04-07
Sa: 2017-04-01

Change $2 to $NF in the awk statement to get the date of the last occurence of each day in a month.

Answer 4

You can just list all days in a next month with weekdays:

# for i in `seq 1 93`; do date '+%Y-%m-%d %w' -d "+$((i - 31)) days"; done | sed 's|0$|7|g' | grep `date +"%Y-%m" --date="$(date +%Y-%m-15) 1 month"`
2021-02-01 1
2021-02-02 2
2021-02-03 3
2021-02-04 4
2021-02-05 5
2021-02-06 6
2021-02-07 7
2021-02-08 1
2021-02-09 2
2021-02-10 3
2021-02-11 4
2021-02-12 5
2021-02-13 6
2021-02-14 7
2021-02-15 1
2021-02-16 2
2021-02-17 3
2021-02-18 4
2021-02-19 5
2021-02-20 6
2021-02-21 7
2021-02-22 1
2021-02-23 2
2021-02-24 3
2021-02-25 4
2021-02-26 5
2021-02-27 6
2021-02-28 7

Append this to get first Sunday of the month: | grep 7$ | head -n 1

That's it

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Off topic: get last Friday of the month: | grep 5$ | tail -n 1

Off topic: get something for this month, change 1 month to 0 month