Does "freshening" a zip file with the -FS option change the modification time of the file?

Question

I have a zip file that I use as a backup for my work. I use the "freshen" option (-FS) whenever I want to update my backup file. However, the file shows the date of last modification as being the date I originally created the file, rather than any of the several times since I have "freshened" the file. Is this normal behavior?

Answer 1

Unix doesn't have a create date, so when you update these files in your .zip you're updating them based on their modification date, which according to the zip man page is normal behavior.

excerpt

The new File Sync option (-FS) is also considered a new mode, though it 
is similar to update.  This mode synchronizes the archive with the files on 
the OS, only replacing files in the archive if the file time or size of the 
OS file is different, adding new files, and deleting entries from the 
archive where there is no matching file.  As this mode can delete entries 
from  the  archive,  consider making a backup copy of the archive.

Example

Say we have the following 3 files:

$ touch file1 file2 file3

We add them to a ZIP file.

$ zip file.zip file{1..3}
  adding: file1 (stored 0%)
  adding: file2 (stored 0%)
  adding: file3 (stored 0%)

Some time passes and file3 gets updated.

$ touch file3

Now we update the ZIP file.

$ zip -FS file.zip file{1..3}
updating: file3 (stored 0%)

Checking the ZIP file we see the times for the files is now like so:

$ unzip -l file.zip 
Archive:  file.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  07-12-2014 02:59   file1
        0  07-12-2014 02:59   file2
        0  07-12-2014 03:00   file3
---------                     -------
        0                     3 files

If we create a temporary directory and unpack the ZIP file within:

$ mkdir temp; cd temp

$ unzip ../file.zip 
Archive:  ../file.zip
 extracting: file1                   
 extracting: file2                   
 extracting: file3                   

The contents of this directory are as follows:

$ ls -l
total 0
-rw-rw-r--. 1 saml saml 0 Jul 12 02:59 file1
-rw-rw-r--. 1 saml saml 0 Jul 12 02:59 file2
-rw-rw-r--. 1 saml saml 0 Jul 12 03:00 file3

And if we use the stat command to check out file3:

$ stat file3
  File: ‘file3’
  Size: 0           Blocks: 0          IO Block: 4096   regular empty file
Device: fd02h/64770d    Inode: 17307675    Links: 1
Access: (0664/-rw-rw-r--)  Uid: ( 1000/    saml)   Gid: ( 1000/    saml)
Context: unconfined_u:object_r:user_home_t:s0
Access: 2014-07-12 03:00:16.000000000 -0400
Modify: 2014-07-12 03:00:16.000000000 -0400
Change: 2014-07-12 03:01:03.447913554 -0400
 Birth: -

NOTE: Notice there is timestamps for access, modify, and change. The zip command is preserving the access and modify times when you use the -FS switch.

References

• get age of given file
• How to find creation date of file?
• Get file created/creation time?