I have a string in format 20141225093000 which represents Dec 25, 2014 09:30:00 and I want to convert the original format to a unix timestamp format so i can do time operations on it.How would I do this in bash?
I can easily parse out the values with expr but I was hoping to be able to identify a format like YYYYmmddHHMMSS and then convert it based on that.
With GNU date, you can convert YYYY-MM-DDTHH:MM:SS to epoch time (seconds since 1-1-1970) easily, like so:
date -d '2014-12-25T09:30:00' +%s
To do this starting without any delimiters:
in=20141225093000
rfc_form="${in:0:4}-${in:4:2}-${in:6:2}T${in:8:2}:${in:10:2}:${in:12:2}"
epoch_time=$(date -d "$rfc_form" +%s)
You need to transform the string before calling date:
#!/bin/bash
s="20141225093000"
s=$(perl -pe 's/(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})/$1-$2-$3 $4:$5:$6/g' <<< "$s")
date -d "$s" +%s
Yet another way:
perl -MDate::Parse -MPOSIX -le '$s="20141225093000"; $s =~ s/(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})/$1-$2-$3 $4:$5:$6/g ; print str2time($s);'
1419499800
perl, why not do the whole thing there? That way you don't need to depend on GNU date (and will work on non-GNU platforms such as MacOS)... and Perl's date-time libraries will take a format string, so you can do the actual conversion in a shorter/more readable way.
perl but when I see sh bash tags I limit my perl commands to one-liner and avoid using non-core modules which may not be installed.bash tag, none of the functionality you used in perl is anything bash doesn't already have built-in (there's already support for regular expressions with capture and group extraction via the =~ operator and BASH_REMATCH).This Bash function does the conversion with builtins:
# Convert UTC datetime string (YYYY-MM-DD hh:mm:ss) to Unix epoch seconds
function ymdhms_to_epoch
{
local -r ymdhms=${1//[!0-9]} # Remove non-digits
if (( ${#ymdhms} != 14 )) ; then
echo "error - '$ymdhms' is not a valid datetime" >&2
return 1
fi
# Extract datetime components, possibly with leading zeros
local -r year=${ymdhms:0:4}
local -r month_z=${ymdhms:4:2}
local -r day_z=${ymdhms:6:2}
local -r hour_z=${ymdhms:8:2}
local -r minute_z=${ymdhms:10:2}
local -r second_z=${ymdhms:12:2}
# Remove leading zeros from datetime components to prevent them
# being treated as octal values
local -r month=${month_z#0}
local -r day=${day_z#0}
local -r hour=${hour_z#0}
local -r minute=${minute_z#0}
local -r second=${second_z#0}
# Calculate Julian Day Number (jdn)
# (See <http://en.wikipedia.org/wiki/Julian_day>, Calculation)
local -r -i a='(14-month)/12'
local -r -i y=year+4800-a
local -r -i m=month+12*a-3
local -r -i jdn='day+(153*m+2)/5+365*y+(y/4)-(y/100)+(y/400)-32045'
# Calculate days since the Unix epoch (1 Jan. 1970)
local -r -i epoch_days=jdn-2440588
local -r -i epoch_seconds='((epoch_days*24+hour)*60+minute)*60+second'
echo $epoch_seconds
return 0
}
Example usage:
$ ymdhms_to_epoch '1970-01-01 00:00:00'
0
$ ymdhms_to_epoch '2014-10-18 00:10:06'
1413591006
$ ymdhms_to_epoch '2014-12-25 09:30:00'
1419499800
var=${var#0} and prepend them by 10#: declare -i v='36525*10#var'date -S - +%s for this! But as a background co-process: Convert date time string to epoch in BashGNU awk:
gawk -v t=20141225093000 'BEGIN {gsub(/../, "& ", t); sub(/ /,"",t); print mktime(t)}'
If GNU date is not available, then it's likely GNU awk may not be. Perl probably has the highest chance of being available. This snippet uses strptime so you don't have to parse the time string at all:
perl -MTime::Piece -E 'say Time::Piece->strptime(shift, "%Y%m%d%H%M%S")->epoch' 20141225093000
datecommand. Are you targeting only platforms with GNU date, or do you need to support other, incompatible versions ofdate(such as MacOS's BSD-derived implementation)?