Reformat date in text file (.csv) with sed and date - shell

Question

This is the input .csv file
"item1","10/11/2017 2:10pm",1,2, ...
"item2","10/12/2017 3:10pm",3,4, ...
.
.
.
Now, I want to convert the second column (date) to this specific format
date -d '10/12/2017 2:10pm' +'%Y/%m/%d %H:%M:%S', so that "10/12/2017 2:10pm" converts to "2017/10/12 14:10:00"
Expecting output file
"item1","2017/10/11 14:10:00",1,2, ...
"item2","2017/10/12 15:10:00",3,4, ...
.
.
.
I know it can be done by using bash or python, but I want to do it in one-line command. Any ideas? Is there a way to pass date result to sed?

Answer 1

One-liner awk approach.
awk -F',' '{gsub(/"/,"",$2); cmd="date -d\""$2"\" +\\\"%Y/%m/%d\\ %T\\\"";
cmd |getline $2; close(cmd) }1' OFS=, infile #>>outfile
"item1","2017/10/11 14:10:00",1,2, ...
"item2","2017/10/12 15:10:00",3,4, ...
This will output changes in your Terminal, you need to redirect the output to a file if you need record the output or use FILENAME to redirect the output to the input infile itself.
awk -F',' '{gsub(/"/,"",$2); cmd="date -d\""$2"\" +\\\"%Y/%m/%d\\ %T\\\"";
cmd |getline $2; close(cmd); print >FILENAME }' OFS=, infile
Or with GNU awk implementations which does support -i inplace identifier for in-place replace. see 'awk' save modifications in place

Answer 2

You can do it in one line, but that begs the question -- "How long of a line do you want?" Since you have it labeled 'shell' and not bash, etc., you are a bit limited in your string handling. POSIX shell provides enough to do what you want, but it isn't the speediest remedy. You are either going to end up with an awk or sed solution that calls date or a shell solution that calls awk or sed to parse old date from the original file and feeds the result to date to get your new date. You will have to work out which provides the most efficient remedy.
As far as the one-liner goes, you can do something similar to the following while remaining POSIX compliant. It simply uses awk to get the 2nd field from the file, pipes the result to a while loop which uses expr length "$field" to get the length and uses that within expr substr "$field" "2" <length expression - 2> to chop the double-quotes from the end of the original date olddt, followed by date -d "$olddt" +'%Y/%m/%d %H:%M:%S' to get newdt and finally sed -i "s;$olddt;$newdt;" to perform the substitution in place. Your one-liner (shown with auto line-continuations for readability)
$ awk -F, '{print $2}' timefile.txt |
while read -r field; do
olddt="$(expr substr "$field" "2" "$(($(expr length "$field") - 2))")";
newdt=$(date -d "$olddt" +'%Y/%m/%d %H:%M:%S');
sed -i "s;$olddt;$newdt;" timefile.txt; done
Example Input File
$ cat timefile.txt
"item1","10/11/2017 2:10pm",1,2, ...
"item2","10/12/2017 3:10pm",3,4, ...
Resulting File
$ cat timefile.txt
"item1","2017/10/11 14:10:00",1,2, ...
"item2","2017/10/12 15:10:00",3,4, ...
There are probably faster ways to do it, but this is a reasonable length one-liner (relatively speaking).

Answer 3

Revised less ugly sed method:
sed 's/^.*,"\|",.*//g;h;s#.*#date "+%Y/%m/%d %T" -d "&"#e;H;g;s#\n\|$#,#g;s/^/s,/' input.csv | sed -f - input.csv
Spread out, (it works the same):
sed 's/^.*,"\|",.*//g
h;
s#.*#date "+%Y/%m/%d %T" -d "&"#e;
H;
g;
s#\n\|$#,#g;
s/^/s,/' input.csv | sed -f - input.csv
Output:
"item1","2017/10/11 14:10:00",1,2, ...
"item2","2017/10/12 15:10:00",3,4, ...
How it works:
The first sed block uses the evaluate command to run date, the output of which is used to generate some new sed substitute commands. To show the new s commands, temporarily replace the shell script | pipe with a # comment:
s,10/11/2017 2:10pm,2017/10/11 14:10:00,
s,10/12/2017 3:10pm,2017/10/12 15:10:00,
These are piped to the second sed.