Convert hh:mm:ss into seconds in Bash-CodePudding

I would like to convert times into seconds aka:

00:24:56 = 25 * 60   56 = 1556
01:00:00 = 1 * 60 * 60 = 3600

I had been using: date -d$element %s but this of course returns the current date and time in seconds.

CodePudding user response：

Simply specify the starting date of Unix time (also known as "Epoch") in the UTC time zone (shorthand Z):

time=00:24:56
date -d "1970-01-01 $time Z"  %s
# prints 1496

CodePudding user response：

The title says in Bash, so I’m going to assume that no external tools (such as date) are allowed. At which point I would do something old-fashioned — like a calculation with a base-60 number:

#!/usr/bin/env bash
set -euo pipefail
shopt -s extglob

to_seconds() {
  local -a digits
  IFS=: digits=($1)
  local -air digits=("${digits[@]## (0)}")  # else ^0 means octal
  local -i i="$((${#digits[@]} - 1))" result=0 order=1
  for ((;;)); do
    ((result  = digits[i] * order)) || :
    ((--i < 0)) && break || :
    ((order *= 60))
  done
  echo "$((result))"
}

As a side note, the base#number integer syntax is easy to find in the Bash man page, but I have never found a way to (ab)use it nicely. On the other hand, there is always an obvious and ugly way to use that syntax:

#!/usr/bin/env bash
set -euo pipefail
shopt -s extglob

declare -ar DIGITS=(0 1 2 3 4 5 6 7 8 9
                    a b c d e f g h i j
                    k l m n o p q r s t
                    u v w x y z A B C D
                    E F G H I J K L M N
                    O P Q R S T U V W X)

to_seconds() {
  local -a digits
  IFS=: digits=($1)
  local -air digits=("${digits[@]## (0)}")  # else ^0 means octal
  local -i digit
  local result=
  for digit in "${digits[@]}"; do
    result ="${DIGITS[digit]}"
  done
  echo "$((60#"$result"))"  # Magic! Ugliness!
}

Examples:

to_seconds 01:09:09  # 4149
to_seconds 01:11:09  # 4269
to_seconds 23:09:00  # 83340
to_seconds 00:59:59  # 3599
to_seconds 00:09:09  # 549
to_seconds 11:09:09  # 40149
to_seconds 23:59:59  # 86399