shell script that displays the processes launched in the background - linux

Question

I have a little problem here. I am trying to write a script shell that shows background processes, but at a certain date. The date is a positional parameter. I've searched on Internet about the date validation, but all the info I found got me confused. I'm fairly new at this so a little help would be appreciated.
How do I verify if the date parameter is in a valid format in my shell script?

Answer 1

you can use regex :
#! /bin/bash
isDateInvalid()
{
DATE="${1}"
# Autorized separator char ['space', '/', '.', '_', '-']
SEPAR="([ \/._-])?"
# Date format day[01..31], month[01,03,05,07,08,10,12], year[1900..2099]
DATE_1="((([123][0]|[012][1-9])|3[1])${SEPAR}(0[13578]|1[02])${SEPAR}(19|20)[0-9][0-9])"
# Date format day[01..30], month[04,06,09,11], year[1900..2099]
DATE_2="(([123][0]|[012][1-9])${SEPAR}(0[469]|11)${SEPAR}(19|20)[0-9][0-9])"
# Date format day[01..28], month[02], year[1900..2099]
DATE_3="(([12][0]|[01][1-9]|2[1-8])${SEPAR}02${SEPAR}(19|20)[0-9][0-9])"
# Date format day[29], month[02], year[1904..2096]
DATE_4="(29${SEPAR}02${SEPAR}(19|20(0[48]|[2468][048]|[13579][26])))"
# Match the date in the Regex
if ! [[ "${DATE}" =~ "^(${DATE_1}|${DATE_2}|${DATE_3}|${DATE_4})$" ]]
then
echo -e "ERROR - '${DATE}' invalid!"
else
echo "${DATE} is valid"
fi
}
echo
echo "Exp 1: "`isDateInvalid '12/13/3550'`
echo "Exp 2: "`isDateInvalid '12/11/20322'`
echo "Exp 3: "`isDateInvalid '12 01 2000'`
echo "Exp 4: "`isDateInvalid '28-02-2014'`
echo "Exp 5: "`isDateInvalid '12_02_2002'`
echo "Exp 6: "`isDateInvalid '12.10.2099'`
echo "Exp 7: "`isDateInvalid '31/11/2020'`

Answer 2

If I'm understanding correctly, you want to input a date and filter background processes by that input and you are looking for a way to validate the input using the shell?
If you can break out the year/month/day into a slash-separated format, you can use the date command to test if the date stamp is valid. This runs under bash, other shells may be different
bad
$ echo -n "year :"; read year; echo -n "month :"; read month; echo -n "day :"; read day; date -d "$year/$month/$day" || echo "Not a valid date"
year :9999
month :32
day :32
date: invalid date ‘9999/32/32’
Not a valid date
good
$ echo -n "year :"; read year; echo -n "month :"; read month; echo -n "day :"; read day; date -d "$year/$month/$day" || echo "Not a valid date"
year :2020
month :3
day :23
Mon Mar 23 00:00:00 CDT 2020