Bash script assistance with renaming file using existing parts of filename - bash

Question

I'm looking for help with a bash script to do some renaming of files for me. I don't know much about bash scripting, and what I have read is overwhelming. It's a lot to know/understand for the limited applications I will probably have.
In Dropbox, my media files are named something like:
Photo Jul 04, 5 49 44 PM.jpg
Video Jun 22, 11 21 00 AM.mov
I'd like them to be renamed in the following format: 2015-07-04 1749.ext
Some difficulties:
The script has to determine if AM or PM to put in the correct 24-hour format
The year is not specified; it is safe to assume the current year
The date, minute and second have a leading zero, but the hour does not; therefore the position after the hour is not absolute
Any assistance would be appreciated. FWIW, I'm running MacOS.

Answer 1

Mac OSX
This uses awk to reformat the date string:
for f in *.*
do
new=$(echo "$f" | awk -F'[ .]' '
BEGIN {
split("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec",month)
for (i in month) {
nums[month[i]]=i
}
}
$(NF-1)=="PM" {$4+=12;}
{printf "%s 2015-%02i-%02i %02i%02i.%s",$1,nums[$2],$3,$4,$5,$8;}
')
mv "$f" "$new"
done
After the above was run, the files are now named:
$ ls -1 *.*
Photo 2015-07-04 1749.jpg
Video 2015-06-22 1121.mov
The above was tested on GNU awk but I don't believe that I have used any GNU-specific features.
GNU/Linux
GNU date has a handy feature for interpreting human-style date strings:
for f in *.*
do
prefix=${f%% *}
ext=${f##*.}
datestr=$(date -d "$(echo "$f" | sed 's/[^ ]* //; s/[.].*//; s/ /:/3; s/ /:/3; s/,//')" '+%F %H%M')
mv "$f" "$prefix $datestr.$ext"
done
Here is an example of the script in operation:
$ ls -1 *.*
Photo Jul 04, 5 49 44 PM.jpg
Video Jun 22, 11 21 00 AM.mov
$ bash script
$ ls -1 *.*
Photo 2015-07-04 1749.jpg
Video 2015-06-22 1121.mov

Answer 2

While not a simple parse and reformat for date, it isn't that difficult. The bash string tools of parameter expansion/substring removal are all you need to parse the pieces of the date into a format that date can use to output a new date string in the format for use in a filename. (see String Manipulation ) date -d is used to generate a new date string based on the contents of the original filename.
Note: the following presumes the dropbox filenames are in the format you have specified. (it doesn't care what the first part of the name or extension is as long as it matches the format you have specified) Here is an example of properly isolating the pieces of the filename needed to generate a date in the format specified)
Further, all spaces have been removed from the filename. While you originally showed a space between the day and hours, I will not provide an example of poor practice by inserting a space in a filename. As such, the spaces have been replaced with '_' and '-':
#!/bin/bash
# Photo Jul 04, 5 49 44 PM.jpg
# Video Jun 22, 11 21 00 AM.mov
# fn="Photo Jul 04, 5 49 44 PM.jpg"
fn="Video Jun 22, 11 21 00 AM.mov"
ext=${fn##*.} # determine extension
prefix=${fn%% *} # determine prefix (Photo or Video)
datestr=${fn%.${ext}} # remove extension from filename
datestr=${datestr#${prefix} } # remove prefix from datestr
day=${datestr%%,*} # isolate Month and date in day
ampm=${datestr##* } # isloate AM/PM in ampm
datestr=${datestr% ${ampm}} # remove ampm from datestr
timestr=${datestr##*, } # isolate time in timestr
timestr=$(tr ' ' ':' <<<"$timestr") # translate spaces to ':' using herestring
cmb="$day $timestr $hr" # create combined date/proper format
## create date/time string for filename
datetm=$(date -d "$cmb" '+%Y%m%d-%H%M')
newfn="${prefix}_${datetm}.${ext}"
## example moving of file to new name
# (assumes you handle the path correctly)
printf "mv '%s' %s\n" "$fn" "$newfn"
# mv "$fn" "$newfn" # uncomemnt to actually use
exit 0
Example/Output
$ bash dateinfname.sh
mv 'Video Jun 22, 11 21 00 AM.mov' Video_20150622-1121.mov