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I searched for a standard format for using a date/time as part of a file name and was unable to come up with anything.

My question is two parts:

Is using time stamps to enforce unique in file names a poor practice?

I could get the time from the creation date and serialize the file names (file0001.bak, file0002.bak, etc) but just including the time stamp lets perform file operations such as mv 2011-01* somewhere/. Is there a downside to using this type of naming system?

The format I am using is YYYY-mm-dd_HH-MM-SS.

Is there a better format I should be using?

With this format should i be concerned with file system compatibility, str_to_date_parsing concerns, etc?

Thanks!

edit:

I might have wanted to leave out the enforce uniqueness bit since it's a single user generating backup using a cronjob (there shouldn't be any concurrency problems).

dting
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6 Answers6

83

You should consider ISO 8601 format (2013-04-01T13:01:02). Yes there are standards for these things. The colons and hyphens may be omitted.

The format string I usually use is %Y%m%dT%H%M%S yielding 20130401T130102. Depending on requirements I omit values from the left. In a bash script I get the date with a line like:

LOGDATE=$(date +%Y%m%dT%H%M%S)
Community
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BillThor
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12

I searched for a standard format for using a date/time as part of a file name and was unable to come up with anything.

My question is two parts:

Is using a time stamp to enforce unique file names a poor practice?

No, it's fine.

I could get the time from the creation date and serialize the file names (file0001.bak, file0002.bak, etc)

Numbering them sequentially is more work. Think of the timestamp as an increasing but non-sequential numbering.

but just including the time stamp lets perform file operations such as mv 2011-01* somewhere/. Is there a downside to using this type of naming system?

No, it's done all the time.

The format I am using is YYYY-mm-dd_HH-MM-SS.

That's good, because they will sort in chronological order. I would lose the underscore, just because it's easier to type a hyphen.

Is there a better format I should be using?

Not really.

Community
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kevin cline
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5

The format you are using is fine but if you want uniqueness and the time has no other meaning you may have concurrency problem in your application if the application is used by multiple users in the same time and they all cause files to be created in the same folder. If you just want uniqueness you may consider generation of GUID and removing any invalid characters like curly braces and dashes and use it as the file name.

M.Sameer
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4

It depends on your application. Sometimes a timestamp like the one your described can be used. Sometimes when name collision is a concern you can use a GUID generator.

grokus
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Using ISO 8601 format also lets you sort the files by date (presuming they all have the same prefix).

http://www.iso.org/iso/support/faqs/faqs_widely_used_standards/widely_used_standards_other/date_and_time_format.htm
http://en.wikipedia.org/wiki/ISO_8601

Tangurena
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The FBI has a "single" user problem of backing up 100 million criminal arrest fingerprints that they receive from all police everywhere...

...they start with the date: yyyymmdd

I don't know how they continue. I continue with hhmm and for me that does it.

Using GMT / Zulu sounds like an excellent idea for a global solution. Personally I use ET, and the FBI "personally" uses ET as well since that's where they are headquartered.

dave
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