How to test for file update - UNIX for Advanced & Expert Users

CraigMoore · #1 (**permalink**) 10-07-2008

I would like to test if a file has been updated from a website located here:

I-BlockList

Is there anyway to do this from the command line (I'd like to add it to a script). I'd just like to either:

(a) See if the file has been updated by looking at the file's 'Date Modified' or

(b) Compare the file size with one I have downloaded earlier.

Of course the file is located on a remote server so you can't use the usual 'ls' commands, and if you use wget, then you'll download it, which may not be necessary if the file hasn't be updated...

Thanks in advance for your help.

Craig

otheus · #2 (**permalink**) 10-07-2008

The utility "wget" already does what you want to do. Check it out using the -N option. If the copy you have is older than the timestamp the webserver gives for the specified URL, a new copy is downloaded. If the file sizes do not match, a new copy is downloaded.

If you don't want it to actually download, but see what it would, do, you can use --spider. Then it reports what it would have done:

Code:

$ wget -N -v http://www.keepalived.org/documentation.html
--16:35:14--  http://www.keepalived.org/documentation.html
Resolving www.keepalived.org... 213.228.1.83
Connecting to www.keepalived.org|213.228.1.83|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 5035 (4.9K) [text/html]
The sizes do not match (local 0) -- retrieving.

--16:35:15--  http://www.keepalived.org/documentation.html
Reusing existing connection to www.keepalived.org:80.
HTTP request sent, awaiting response... 200 OK
Length: 5035 (4.9K) [text/html]
Saving to: `documentation.html'

100%[=======================================>] 5,035       --.-K/s   in 0.07s

16:35:15 (68.6 KB/s) - `documentation.html' saved [5035/5035]

[otheus] ~$ touch documentation.html
[otheus] ~$ wget -N -v http://www.keepalived.org/documentation.html
--16:36:08--  http://www.keepalived.org/documentation.html
Resolving www.keepalived.org... 213.228.1.83
Connecting to www.keepalived.org|213.228.1.83|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 5035 (4.9K) [text/html]
Server file no newer than local file `documentation.html' -- not retrieving.

[otheus] ~$ echo test >> documentation.html
Change the file size of documentation.html
[otheus] ~$ wget --spider -N -v http://www.keepalived.org/documentation.html
--16:36:27--  http://www.keepalived.org/documentation.html
Resolving www.keepalived.org... 213.228.1.83
Connecting to www.keepalived.org|213.228.1.83|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 5035 (4.9K) [text/html]
The sizes do not match (local 0) -- retrieving.

--16:36:27--  http://www.keepalived.org/documentation.html
Reusing existing connection to www.keepalived.org:80.
HTTP request sent, awaiting response... 200 OK
Length: 5035 (4.9K) [text/html]
200 OK

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