get age of given file

Question

How can I get the age of a given file in, at least, days?

I'm well aware of ls -lh and similar commands. I want something that will work sort of like this:

getfage <FILE> # prints out '12d' (12 days)

Also, this needs to be somewhat cross-platform since I'd also like to use this under Mac OS X, but the primary use-case is on my Linux-box.

NOTE

Since Linux doesn't track creation time, I'm looking for two-fold solution: one for mtime (linux)--that is the last time said file was modified--and one for Mac OS X, which can either deal with mtime or creation time.

Answer 1

OSX keeps track of file creation, but most other unices don't, so there's no way to know the elapsed time since the file creation. You can obtain the elapsed time since its last modification on just about any operating system.

There's no portable shell utility to retrieve a file's modification time, except ls which has output that's nigh-impossible to parse. Under Linux, the following command prints the age of a file:

echo $(($(date +%s) - $(date +%s -r "$filename"))) seconds
echo $((($(date +%s) - $(date +%s -r "$filename")) / 86400)) days

Under Linux, you can use stat -c %Y -- "$filename" as a synonym of date +%s -r "$filename".

OSX's date and stat commands are different. You can use the following command:

echo $(($(date +%s) - $(stat -t %s -f %m -- "$filename"))) seconds
echo $((($(date +%s) - $(stat -t %s -f %m -- "$filename")) / 86400)) days

Non-embedded Linux systems and OSX have Perl installed by default.

perl -l -e 'print -M $ARGV[0], " days"' "$filename"
perl -l -e 'print 86400 * -M $ARGV[0], " seconds"' "$filename"
perl -l -e '$mtime = (stat($ARGV[0]))[9]; print time - $mtime, " seconds"' -- "$filename"

Answer 2

Unix doesn't keep track of a creation date. The only information that's available is typically the last times the files was:

1. Accessed
2. Modified
3. Changed

• Access - the last time the file was read
• Modify - the last time the file was modified (content has been modified)
• Change - the last time meta data of the file was changed (e.g. permissions)

(From this answer)

You can get dates related to a particular file using the stat command.

Example

$ stat ffmpeg 
  File: `ffmpeg'
  Size: 19579304    Blocks: 38248      IO Block: 4096   regular file
Device: fd02h/64770d    Inode: 10356770    Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (  500/    saml)   Gid: (  501/    saml)
Access: 2013-11-26 10:49:09.908261694 -0500
Modify: 2013-11-02 17:05:13.357573854 -0400
Change: 2013-11-02 17:05:13.357573854 -0400

OSX and HFS

If you're using OSX the filesystem that's used under that Unix is HFS. This is one of the few (that I'm aware of) that keeps the creation date within the filesystem, along with modification time etc. similar to other Unixes.

excerpt

A File Record stores a variety of metadata about the file including its CNID, the size of the file, three timestamps (when the file was created, last modified, last backed up), the first file extents of the data and resource forks and pointers to the file's first data and resource extent records in the Extent Overflow File. The File Record also stores two 16 byte fields that are used by the Finder to store attributes about the file including things like its creator code, type code, the window the file should appear in and its location within the window.

Timestamps

Time stamps are always maintained in the filesystem, so you're limited by whatever time tracking is offered through them (EXT3, EXT4, XFS, etc.).

Filesystems

If you're ever curious take a look at this Wikipedia topic titled: Comparison of file systems. It has the most extensive list of filesytems I'm aware of along with a nice table of the various features and the status of whether it's supported or not within a given filesystem.

References

• How to find creation date of file?
• How do I do a ls and then sort the results by date created?
• List files created on Sundays
• Get file created/creation time?
• Why does Unix time start at 1970-01-01?

Answer 3

Based on answer by Gilles, here is a bash function that returns file age in seconds or error.

function fileAge
{
    local fileMod
    if fileMod=$(stat -c %Y -- "$1")
    then
        echo $(( $(date +%s) - $fileMod ))
    else
        return $?
    fi
}

Answer 4

stat -c %Y <filename>

look at man stat for -c (format) options

Answer 5

You can use stat -f%B, ls -lU, or mdls -n kMDItemFSCreationDate to see the creation (birth) time in OS X:

$ stat -f%B file
1402340803
$ ls -lU file
-rw-r--r--  1 admin  staff  108514 Jun  9 22:06 file
$ mdls -n kMDItemFSCreationDate file
kMDItemFSCreationDate = 2014-06-09 19:06:43 +0000
$ echo $((($(date +%s)-$(stat -f%B file))/86400))
10

Answer 6

For standard Unix, stat -c %Y as seen in other answers gets you the 'last modified' time. But for some circumstances you might want the 'inode change time' - this is when the metadata last changed. It gets updated when you first make the file and then when you do things like chmod (which, most of the time, you won't be doing - so in many circumstances it stays as the original creation time). That can be output with stat -c %Z.

Answer 7

If you just want output as 12d or 12 days I use this...

filename=/path/to/your/file.txt
now=$(date +%s)
modified=$(date -r "$filename" "+%s")
delta=$((now-modified))
printf 'Created %d days ago\n' $((delta/86400))
printf 'Created %dh:%dm:%ds ago\n' $((delta/3600)) $((delta%3600/60)) $((delta%60))

Answer 8

Came across this today.

The Linux stat command now seems to have a birth date:

    $ stat myfile.ext
  File: myfile.ext
  Size: 4091        Blocks: 8          IO Block: 4096   regular file
Device: 0,38    Inode: 5476021     Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/chandana)   Gid: ( 1000/chandana)
Context: unconfined_u:object_r:user_home_t:s0
Access: 2022-11-11 14:07:03.744610297 +1100
Modify: 2022-11-11 14:06:45.516562357 +1100
Change: 2022-11-11 14:06:45.519562365 +1100
 Birth: 2022-11-11 14:06:45.516562357 +1100