Age calculation program with completed months and days - bash

Question

Good afternoon I have a program in bash to calculate the age by entering the data of the year, month and day of birth. But I would also like to calculate the completed months and days. What would be the conditions that I should add to my code. Please help
echo "Enter your year of birth"
read a_nac
echo "Enter your month of birth"
read m_nac
echo "Enter your day of birth"
read d_nac
echo "-----------Birth Date---------"
echo $d_nac $m_nac $a_nac
a_act=$(date +%Y)
m_act=$(date +%m)
d_act=$(date +%d)
echo "-----------Current Date-------------"
echo $d_act $m_act $a_act
let edad=$a_act-$a_nac
if [ $m_act -lt $m_nac ]; then
((edad--))
elif [ $m_nac -eq $m_act -a $d_act -lt $d_nac ]; then
((edad--))
fi
echo "-----------Age-------------------"
echo "You have" $edad "years"

Answer 1

It's a bit complex to find a generic solution. For the dates after the epoch we can convert both the dates with date +%s and make a plain subtraction.
A more generic solution follows:
echo "Enter your year of birth"
read a_nac
echo "Enter your month of birth"
read m_nac
echo "Enter your day of birth"
read d_nac
echo "-----------Birth Date---------"
echo $d_nac $m_nac $a_nac
a_act=$(date +%Y)
m_act=$(date +%-m)
d_act=$(date +%-d)
echo "-----------Current Date-------------"
echo $d_act $m_act $a_act
let years=$a_act-$a_nac
if [ $m_act -lt $m_nac ]; then
((years--))
let months=$m_nac-$m_act
elif [ $m_act -ge $m_nac ]; then
let months=$m_act-$m_nac
elif [ $m_nac -eq $m_act -a $d_act -lt $d_nac ]; then
((years--))
fi
if [ $d_act -lt $d_nac ]; then
((months--))
let days=30-$d_nac+$d_act
else
let days=$d_act-$d_nac
fi
echo "-----------Age-------------------"
echo "You have $years years, $months months, $days days"
The line
let days=30-$d_nac+$d_act
does not take into account that not all the months have 30 days and the case of leap months. The correction is left to the reader ;)