bashのファイルのタイムスタンプ比較処理がよくわからなかったので調べてみた ref: http://qiita.com/ikeisuke/items/2cc48db12baeab932450

file0.txt

[ $A -nt $B]:
  1: $A and $B do not exist ($A=, $B=)
  0: $A exists, $B does not exist ($A=2016-08-19 14:43:18.214264727 +0900, $B=)
  1: $A dose not exist. $B exists ($A=, $B=2016-08-19 14:43:18.214264727 +0900)
  1: $A is older than $B ($A=2016-08-19 14:43:18.218264799 +0900, $B=2016-08-19 14:43:19.218282884 +0900)
  1: $A is older than $B(0.1sec) ($A=2016-08-19 14:43:19.222282957 +0900, $B=2016-08-19 14:43:19.322284769 +0900)
  0: $A is newer than $B ($A=2016-08-19 14:43:20.326302931 +0900, $B=2016-08-19 14:43:19.326284841 +0900)
  1: $A is newer than $B(0.1sec) ($A=2016-08-19 14:43:20.434304881 +0900, $B=2016-08-19 14:43:20.330303003 +0900)
  1: $A and $B is same timestamp ($A=2016-08-19 14:43:20.434304881 +0900, $B=2016-08-19 14:43:20.434304881 +0900)
[ $A -ot $B]:
  1: $A and $B do not exist ($A=, $B=)
  1: $A exists, $B does not exist ($A=2016-08-19 14:43:20.438304953 +0900, $B=)
  0: $A dose not exist. $B exists ($A=, $B=2016-08-19 14:43:20.442305026 +0900)
  0: $A is older than $B ($A=2016-08-19 14:43:20.442305026 +0900, $B=2016-08-19 14:43:21.446323193 +0900)
  1: $A is older than $B(0.1sec) ($A=2016-08-19 14:43:21.450323265 +0900, $B=2016-08-19 14:43:21.550325069 +0900)
  1: $A is newer than $B ($A=2016-08-19 14:43:22.554343230 +0900, $B=2016-08-19 14:43:21.554325141 +0900)
  1: $A is newer than $B(0.1sec) ($A=2016-08-19 14:43:22.658345114 +0900, $B=2016-08-19 14:43:22.558343302 +0900)
  1: $A and $B is same timestamp ($A=2016-08-19 14:43:22.662345187 +0900, $B=2016-08-19 14:43:22.662345187 +0900)

file1.txt

#!/bin/bash

A=/tmp/filea
B=/tmp/fileb

function cleanup() {
  [ -f $A ] && rm -f $A
  [ -f $B ] && rm -f $B
}
function show_nt_result() {
  local TIMEA TIMEB
  [ -f $A ] && TIMEA=$(stat $A --format %y)
  [ -f $B ] && TIMEB=$(stat $B --format %y)
  [ $A -nt $B ]
  echo "  $?: $1 (\$A=$TIMEA, \$B=$TIMEB)"
}
function show_ot_result() {
  local TIMEA TIMEB
  [ -f $A ] && TIMEA=$(stat $A --format %y)
  [ -f $B ] && TIMEB=$(stat $B --format %y)
  [ $A -ot $B ]
  echo "  $?: $1 (\$A=$TIMEA, \$B=$TIMEB)"
}

echo '[ $A -nt $B]: '

cleanup
show_nt_result '$A and $B do not exist'

cleanup
touch $A
show_nt_result '$A exists, $B does not exist'

cleanup
touch $B
show_nt_result '$A dose not exist. $B exists'

cleanup
touch $A
sleep 1
touch $B
show_nt_result '$A is older than $B'

cleanup
touch $A
sleep 0.1
touch $B
show_nt_result '$A is older than $B(0.1sec)'

cleanup
touch $B
sleep 1
touch $A
show_nt_result '$A is newer than $B'

cleanup
touch $B
sleep 0.1
touch $A
show_nt_result '$A is newer than $B(0.1sec)'

cleanup
touch $A
touch $B -r $A
show_nt_result '$A and $B is same timestamp'

echo '[ $A -ot $B]: '

cleanup
show_ot_result '$A and $B do not exist'

cleanup
touch $A
show_ot_result '$A exists, $B does not exist'

cleanup
touch $B
show_ot_result '$A dose not exist. $B exists'

cleanup
touch $A
sleep 1
touch $B
show_ot_result '$A is older than $B'

cleanup
touch $A
sleep 0.1
touch $B
show_ot_result '$A is older than $B(0.1sec)'

cleanup
touch $B
sleep 1
touch $A
show_ot_result '$A is newer than $B'

cleanup
touch $B
sleep 0.1
touch $A
show_ot_result '$A is newer than $B(0.1sec)'

cleanup
touch $A
touch $B -r $A
show_ot_result '$A and $B is same timestamp'