Change date and time format from csv file without using date -d

A pure awk solution (that doesn’t fork off a date command):

awk -F'|' -vOFS='|' '
function fail() {
        printf "Bad data at line %d: ", NR
        print
        next
    }
    {
        if (split($3, date_time, " ") != 3) fail()
        if (split(date_time[1], date, "/") != 3) fail()
        if (split(date_time[2], time, ":") != 3) fail()
        if (time[1] == 12) time[1] = 0
        if (date_time[3] == "PM") time[1] += 12
        $3 = sprintf("%.4d%.2d%.2d %.2d:%.2d:%.2d", date[3], date[1], date[2], time[1], time[2], time[3])
        print
    }'

• -F'|' breaks the input line apart at vertical bars into $1, $2, $3, etc…
• split($3, date_time, " ") breaks the date/time field into three pieces: the date, the time, and the AM/PM indicator.  If there aren’t three pieces, issue an error message and skip the line.
• split(date_time[1], date, "/") splits the date into the month, the day, and the year.
• split(date_time[2], time, ":") splits the time into the hour, the minutes, and the seconds.
• Do some math on the hour; for example, 12:42 AM is 00:42 in 24-hour time.  And of course PM adds 12 hours.
• The sprintf reassembles the year, month, day, hour, minutes, and seconds, with leading zeroes, if necessary.  Assigning this to $3 rebuilds the input line with the reformatted date/time; we then print that.

• Feature: If the input has more than three fields; e.g.,

  Data1|Data2|10/24/2017 8:10:00 AM|Data4|Data5
  

  this script will preserve those extra field(s).

Usage:  A few minor variations:

• Type the above multi-line command, and, at the end of the last line (right after }'), put the name(s) of file(s) you want to process.  You can (of course) use wildcards (e.g., *.csv) here, in addition to or instead of filename(s).
• Same as the above, but after }', say < and a filename.  (You can process only one file at a time this way.)
• Create a script file. 
  • The first line should be #!/bin/sh.  (Or, if you prefer, you can use #!/bin/bash or #!/usr/bin/env bash.  A discussion of the differences between these different “she-bang” lines, and their relative merits and counter-indications, is beyond the scope of this question, but you can find plenty of discourse on the topic if you search.)
  • Then put the above code starting at line 2.
  • At the end of the last line (right after }'),  put "$@" (including the quotes).
  • Save the file.  Let’s assume that you call the script gman.
  • Type chmod +x gman.
  • Type ./gman followed by either a list of filenames and/or wildcards, or by < and a single filename.

Here is one way of doing it assuming infile is your CSV file:

#!/bin/bash

IFS='|'
while read data1 data2 datestr 
do
    newdatestr=$(date -d"$datestr" +"%Y%m%d %T")
    printf "%s|%s|%s\n" "$data1" "$data2" "$newdatestr"
done < infile

with AWK:

save file a.awk:

BEGIN{
    FS="|"
    OFS = FS
}
{
    "date -d '"$3"' +'%Y%m%d %T' " | getline l
    $3 = l
    print $0
}

and run it with your csv file:

awk -f a.awk file.csv

for example, output is :

Data1|Data2|20171024 08:10:00
Data1|Data2|20171024 20:10:00
Data1|Data2|20171024 20:10:00
Data1|Data2|20171024 20:14:00
Data1|Data2|20171024 20:14:00
Data1|Data2|20171024 20:11:00
Data1|Data2|20171024 20:10:06
Data1|Data2|20171024 20:10:06
Data1|Data2|20171024 08:10:50

with this example:

Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:10:00 PM
Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:14:00 PM
Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:11:00 PM
Data1|Data2|10/24/2017 8:10:06 PM
Data1|Data2|10/24/2017 8:10:00 PM
Data1|Data2|10/24/2017 8:10:50 AM

I'd use perl or any language with interface to strptime() and strftime():

perl -MTime::Piece -F'[|]' -lape '
  $F[2] = Time::Piece->strptime($F[2], "%m/%d/%Y %I:%M:%S %p")->
                       strftime("%Y%m%d %T");
  $_ = join "|", @F' < file.csv

Same with zsh:

zmodload zsh/datetime
while IFS='|' read -rA F; do
  strftime -rs t '%m/%d/%Y %I:%M:%S %p' $F[3] &&
    strftime -s 'F[3]' '%Y%m%d %T' $t
  printf '%s\n' "${(j:|:)F}"
done < file.csv

Using GNU date (but not date -d) and a shell like bash that understands process substitutions:

$ cat file
Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:10:00 AM
Data1|Data2|10/24/2017 8:10:00 AM
$ paste -d '|' <( cut -d '|' -f -2 file ) <( date -f <( cut -d '|' -f 3 file ) +'%Y%m%d %T' )
Data1|Data2|20171024 08:10:00
Data1|Data2|20171024 08:10:00
Data1|Data2|20171024 08:10:00
Data1|Data2|20171024 08:10:00
Data1|Data2|20171024 08:10:00

The call to date reads the dates from the cut command, which extracts the third |-delimited column from the given file. It outputs one reformatted date per line of input.

This is then pasted together with the first two columns using paste.

This has the downside that it reads the file twice, but it only calls date once (and without -d).

You could also do this with dateutils, e.g. with the following input:

10/24/2017 8:10:00 AM
10/24/2017 8:10:00 PM
10/24/2017 8:10:00 AM
10/24/2017 8:14:00 PM
10/24/2017 8:10:00 AM
10/24/2017 8:11:00 PM
10/24/2017 8:10:06 PM
10/24/2017 8:10:00 PM
10/24/2017 8:10:50 AM

and the dateconv or dateutils.dconv program:

dateconv -i '%m/%d/%Y %H:%M:%S %p' -f '%Y%m%d %T' < infile

Output:

20171024 08:10:00
20171024 20:10:00
20171024 08:10:00
20171024 20:14:00
20171024 08:10:00
20171024 20:11:00
20171024 20:10:06
20171024 20:10:00
20171024 08:10:50

This can be easily done by using sed's extended regex

I am amazed that no one has given answer using sed

GNU sed's one liner :

sed -r 's/([0-9]{2})\/([0-9]{2})\/([0-9]{4})/\3\1\2/' file_name

Here I used extended regex to capture groups