bash script to generate iso-time from output of older BSD-`ls` - bash

Question

I would like to generate an iso-style time info (YYYY-MM-DDTmm:hh:ss) on
a bsd-ish system with an older ls command (man states it's a
BSD-ls) and no --time-style option. The best I get is
$ ls -lT log.out
-rw-r--r-- 1 admin4 staff 49152 Jul 17 09:38:38 2018 log.out
Is there a simple way to transform this time information within a
bash-script into iso-style?
$ timestamp="$(ls -lT log.out | iso-timestamp-gen)"
Your help will be highly appreciated

Answer 1

first, cut out date part:
DATE=`echo - | cut -f9-12 -d' '`;
then convert it to timestamp using date:
echo `date --date="$DATE" +"%s"`;
the iso-timestamp-gen file:
#!/bin/bash
DATE=`echo - | cut -f9-12 -d' '`;
echo `date --date="$DATE" +"%s"`;

Answer 2

To solve our problem
timestamp="$(ls -lT log.out | iso-timestamp-gen)"
#Hamidreza pointed us into the direktion of the date command: One
of our engineers came up with this slender inline solution:
timestamp=$(date -j -f '%b %e %T %Y' \
"$(ls -lT $f | awk '{ print $6, $7, $8, $9 }')" \
+'%F_%T')
where the variable f contains the name of the file to be considered.
In line 2 awk extracts the date-part (fields 6 upto 9) from the output of ls -lT.
Together with this "DateToConvert" date is fed a matching
input format "%b %e %T %Y"
and the requested output format "%F_%T".
We looked up the conversion specifications in
strftime(3).
Up to now neither of us was aware that you could use date not only for
reading and setting the system clock but also for converting dates from
one format to another format:
date -j -f "${InputFormat}" "${DateToConvert}" +"${OutputFormat}"
With some embarassment we confessed this to each other and
decided to make good use of the new insight.
A couple of hours later we added the following new helper to our toolbox.
It extracts the date from the output of ls -lT and converts it to
other formats. So far we included only the iso-format and a format
which is handy when using the touch(1) command. This list may be expanded in the future.
#!/bin/bash
#
# conv-date-of-llT.sh
# convert date output of ls -lT ($OSTYPE == darwin14)
# - to iso-format YYYY-MM-DD_hh:mm:ss or
# - to "touch" format: [[CC]YY]MMDDhhmm[.SS]
#
# hppo, 2018-07-20
# strip $0 of path and ext
Arg0="${0##*/}" # peel off path
Arg0="${Arg0%%.*}" # peel off ext
USAGE="${Arg0} [ -iso | -touch ]"
# select output format
case "fmt$1" in
fmt|fmt-iso|fmtiso) # YYYY-MM-DD_hh:mm:ss
OutputFormat="%F_%T" ;;
fmt-touch|fmttouch) # YYYYMMDDhhmm
OutputFormat="%Y%m%d%H%M" ;;
*)
1>&2 echo -e "${Arg0}: no such output format '$1'\nUsage: ${USAGE}"; exit 1 ;;
esac
# input: output of "ls -lT file" on darwin-14
# -rwxr-xr-x 1 admin4 staff 387 Jul 17 01:38:24 2018 file
# 1 2 3 4 5 6 7 8 9 10
#
# Field 6 - 9: month(%b) day(%e) time(%T) year(%Y), cf strftime(3)
InputFormat="%b %e %T %Y"
# assume stdin is fed by output of ls -lT
DateToConvert="$(awk '{ print $6, $7, $8, $9 }')"
date -j -f "${InputFormat}" "${DateToConvert}" +"${OutputFormat}"