using cal terminal command for next and previous months

cal -m April
cal -m June

I use the bash shell, and to get the current month, I just type cal and hit return:

NoobiX:~ francine$ cal
May 2009
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

For last month, just add the -m option and the number of the month:

NoobiX:~ francine$ cal -m 4
April 2009
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

One would do the same to get next month. To get the month of a particular year:

NoobiX:~ francine$ cal 10 1943
October 1943
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

I'm not sure what you mean by "i've looked over the support page"--but I just brought up the man page with a "man cal" command. Admittedly man pages can be rather, umm, opaque in figuring out what it is they are trying to tell you. :-0
Francine


Francine
Schwieder

These work for me.

Previous month:
cal -m $(($(date +%m) - 1))

Next month:
cal -m $(($(date +%m) + 1))


Edit:
This may fail in December and January since the 12 + 1 = 13 and 1 - 1 = 0 (neither of which is accepted by cal). The general idea is correct though, you'll just need to add some extra logic to fix the edges.

Message was edited by: Noah Robbin

Here's a version that handles the edge months.

#!/bin/bash
year=$(date +%Y)
month=$(date +%m)
prev=$((month-1))
next=$((month+1))
#display previous month
if [ $prev -eq 0 ] ;
then
 cal 12 $((year-1))
else
 cal $prev $year
fi
#display current month
cal $month $year
#display next month
if [ $next -eq 13 ] ;
then
 cal 1 $((year+1))
else
 cal $next $year
fi

This should handle edge conditions even easier:

cal $(date -v -1m "+%m %Y") # Last month
cal $(date "+%m %Y") # This month
cal $(date -v +1m "+%m %Y") # Next month

Because the date command does all the month/year calculations, including year changes, you do not need to do any conditional shell code.

See

man cal
man date

Thank you, I did not know date did that.

One more thought, is there a good way to do this such that you don't call date more than once. Running this near/at midnight at the end of the month could cause a month to be skipped. (This is more an exercise than answering the original question)

One more thought, is there a good way to do this such that you don't call date more than once. Running this near/at midnight at the end of the month could cause a month to be skipped. (This is more an exercise than answering the original question)

This is as close as I can come, but it is more of a script

#!/bin/sh
D=( $(date "+%m %Y") )
M=${D[0]}
Y=${D[1]}
cal $((M-1 < 1 ? 12 : M-1 )) $((M-1 < 1 ? Y-1 : Y))
cal $M $Y
cal $((M+1 > 12 ? 1 : M+1 )) $((M+1 > 12 ? Y+1 : Y))

Thank you again.