Well, yes, "date --date= ..." doesn't work in the way I would wish
("logically" think about it):https://www.gnu.org/software/coreutils/manual/html_node/General-date-syntax.html parsing any format allowed by date: https://www.gnu.org/software/coreutils/manual/html_node/Date-conversion-specifiers.html which made me think of how/why did I start using my "coblesome" formatting, but there is nothing really that homely about it. Those formatting options are listed right on: date --help $ date --version 2>&1 | head -n 1 date (GNU coreutils) 8.32 Based on to...@tuxteam.de's suggestions I worked around a downright simple hack around those formatting problematics with coreutils date: s00=$(date +%s) dt00=$(date +%Y%m%d%H%M%S) dttm00ISeks="${dt00:0:4}-${dt00:4:2}-${dt00:6:2}T${dt00:8:2}:${dt00:10:2}:${dt00:12:2}+00:00" ISeks00=$(date -d"${dttm00ISeks}" +%s) if [[ $s00 -eq $ISeks00 ]]; then echo "// __ \$ISeks00: |$ISeks00|, \$dttm00ISeks: |${dttm00ISeks}| conversion OK!" else echo "// __ \$s00: |$s00|, \$dt00: |${dt00}|" echo "// __ \$ISeks00: |$ISeks00|, \$dttm00ISeks: |${dttm00ISeks}| conversion NOT OK!" fi # 63 weeks 5 days 11 hours 0 minutes et 43 seconds later s02=$(( s00 + 63*7*24*60*60 + 5*24*60*60 + 11*60*60 + 0*60 + 43)) dt02=$(date --date @${s02} +%Y%m%d%H%M%S) echo "// __ \$s02: |$s02|, \$dt02: |${dt02}|" dttm02ISeks="${dt02:0:4}-${dt02:4:2}-${dt02:6:2}T${dt02:8:2}:${dt02:10:2}:${dt02:12:2}+00:00" ISeks02=$(date -d"${dttm02ISeks}" +%s) if [[ $s02 -eq $ISeks02 ]]; then echo "// __ \$ISeks02: |$ISeks02|, \$dttm02ISeks: |${dttm02ISeks}| conversion OK!" _diffs=$(( s02 - s00 )) _diffISeks=$(( ISeks02 - ISeks00 )) if [[ $_diffs -eq $_diffISeks ]]; then echo "// __ differences also OK!" else echo "// __ differences NOT OK! \$_diffs: |$_diffs|, \$_diffISeks: |${_diffISeks}|" fi else echo "// __ \$s02: |$s02|, \$dt02: |${dt02}|" echo "// __ \$ISeks02: |$ISeks02|, \$dttm02ISeks: |${dttm02ISeks}| conversion NOT OK!" fi thank you, lbrtchx
