How to display each day of a month on a separate line using tr, sed and cal

Question

How to use commands, cal, sed and tr and the pipe to display the numerical days (e.g., 1, 2, 3, etc.) of a month, with each day on a separate line

I've tried:

cal 12 2015| sed '3,7p' | tr -cs "[:alpha:]" "[\n*]" 

and go this output:

December
S
M
Tu
W
Th
F
S

Answer 1

You came close.

1. You need to suppress sed's output before selectively printing lines:

   $ cal 12 2015 | sed -n '3,7p'                             
          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       
   

   Your sed might not have -n. In which case, use d to delete all lines except the ones you want.

2. Your tr command replaces everything except alpahabets - and that includes digits. Just replace spaces:

   $ cal 12 2015 | sed -n '3,7p' | tr -s ' ' '\n'                
   
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   

Answer 2

The range of lines in the sed command by @muru caught my eye. You can do this relying less upon the format of cal:

cal 12 2015 | sed '/[[:alpha:]]/d' | tr ' ' '\n' |sed -e '/^$/d'

POSIX does not specify the format for cal, so the length of the header could vary by implementation.