TOPIC: COMPUTER FILE
Renaming multiple files in Linux
19th August 2012
The Linux and UNIX command mv has a number of limitations, such as not overwriting destination files and not renaming multiple files using wildcards. The only solution to the first that I can find is one that involves combining the cp and rm commands. For the second, there's another command: rename. Here's an example like what I used recently:
rename s/fedora/fedora2/ fedora.*
The first argument in the above command is a regular expression much like what Perl is famous for implementing; in fact, it is Perl-compatible ones (PCRE) that are used. The s before the first slash stands for substitute, with fedora being the string that needs to be replaced and fedora2 being what replaces it. The third command is the file name glob that you want to use, fedora.* in this case. Therefore, all files in a directory named fedora will be renamed fedora2 regardless of the file type. The same sort of operation can be performed for all files with the same extension when it needs to be changed, htm to html, for instance. Of course, there are other uses, but these are handy ones to know.
Command line setting of Windows file attributes
11th February 2012
Aside from permissions that can be set using the cacls command, Windows files have properties like read only, archive and hidden. Of course, these are not the same or as robust as access permissions, but they may have a use in stopping accidental updates to files when you don't have access to use of the cacls command. While you could set these attributes using the properties page of any file, executing the attrib command on the Windows command is more convenient. Here are some possible usage options:
Set the read-only flag on a file:
attrib +r test.txt
Remove the read-only flag from a file (found a use for this one recently):
attrib -r test.txt
Set the archive flag on a file:
attrib +a test.txt
Remove the archive flag from a file:
attrib -a test.txt
Set the hidden only flag on a file:
attrib +h test.txt
Remove the hidden flag from a file:
attrib -h test.txt
Using the /s option and wildcards processes a number of files at a time and /d applies the command to directories. They could come in handy when removing read only attributes (also called bits in places) from files copied from read only optical media, such as CD's and DVD's.
Anquet and VirtualBox Shared Folders: Solving Virtual Machine storage issues between Linux and Windows
18th July 2009
For a while now, I have had Anquet installed in a virtual machine instance of Windows XP, but it has been throwing errors continuously on start up. Perhaps surprisingly, it only dawned upon me recently what might have been the cause. A bit of fiddling revealed that my storing the mapping data Linux side and sharing it into the VM wasn't helping, and copying it to a VM hard drive set things to rights.
This type of thing can also cause problems when it comes to getting Photoshop to save files using VirtualBox's Shared Folders feature too. Untangling the situation is a multi-layered exercise. On the Linux side, permissions need to be in order and that involves some work with chmod (775 is my usual remedy) and chgrp to open things up to the vboxusers group.
Adding in Windows' foibles when it comes to networked drives and their mapping to drive letters brings extra complexity; any shared folders are made visible to Windows in a path of this form: \\vboxsvr\shared_folder_name\. The solution is either a lot of rebooting, extensive use of the net use command, or both. It induces the sort of going and coming that causes copying things over and back as needed to look less involved and more sensible, if a little more manual than might be liked.
Copying only updated and new files
20th October 2008
With Linux/UNIX, the command line remains ever useful and allows you to do all manner of things, including file copying that only adds new files to a destination. Here's a command that accomplishes this on Linux:
cp -urv [source] [destination]
The u switch does the update while r ensures recursion (by default, cp only copies files from a source directory and not anything sitting in subfolders) and v tells the command to tell the user what is happening.
Though buried and hardly promoted, Windows also has its command line and here's what accomplishes a similar result:
xcopy /d /u [source] [destination]
Anything's better than having to approve or reject every instance where source and destination files are the same or, even worse, to overwrite a file when it is not wanted.
Error: User does not have appropriate authorization level for library xxxx
25th June 2008
In a world where write access to a folder or directory is controlled by permission settings at the operating system level, a ready answer for when you get the above message in your log when creating a SAS data set would be to check your access. However, if you are working on Windows and your access seems fine, then SAS' generation of an access error message seems all the more perplexing.
Unlike the more black-and-white world of UNIX and Linux, Windows has other ways to change access that could throw things off from the straight and narrow. One of them, it would appear, is to right-click on the file listing pane in Windows Explorer and select "Customize this folder..." to change how it appears. The strange upshot of this is that a perpetual read-only flag is set for the folder in question, and that flag triggers SAS authorisation errors. The behaviour is very strange and unexpected when you find it, and the quickest and easiest solution sounds drastic. This involves deleting the folder and creating a new one in its place, saving anything that you want to retain in another temporary location. An alternative approach uses the attrib command and is less invasive.
It begs the question as to why Microsoft is re-appropriating a flag used for access purposes to be used to determine whether the HTML components of a folder display have been changed or not. This is very strange stuff and does not look like good software design at all. With all the other problems Microsoft creates for itself, I am not holding my breath until it's fixed, either. There seem to be other things like this waiting to catch you out when using Windows SAS, and a good place to start is SAS' own description of the problem that I have just shared.
Porting SAS files to other platforms and versions
1st October 2007
SAS uses its transport file format to port files between operating and, where the need arises, different software versions. As with many things, there is more than one method to create these transport files: PROC CPORT/CIMPORT and PROC COPY with the XPORT engine. The former method is for within version transfer of SAS files between different operating systems (UNIX to Windows, for instance) and the latter is for cross-version transfer (SAS9 to SAS 8, for example). SAS Institute has a page devoted to this subject which may share more details.
Uses for symbolic links
24th April 2007
UNIX (and Linux) does a wonderful trick with its file and folder shortcuts; it effectively treats them as file and folder transporters that transfer associate a file or folder that exists in one folder hierarchy with another, and it is treated as if it exists in that hierarchy too. For example, the folder named images under /www/htdocs/blog can have a link under /www/htdocs/ that makes it appear that its contents exist in both places without any file duplication. For instance, the pwd command cannot tell a folder from a folder shortcut. To achieve this, I use what are called symbolic links and the following command achieves the outcome in the example:
ln -s /www/htdocs/blog/images /www/htdocs/images
The first file path is the destination for the link, while the second one is that for the link itself. Once, I had a problem with Google Reader not showing up images in its feed displays, so symbolic links rode to the rescue as they did for resolving a similar conundrum that I was encountering when editing posts in my hillwalking blog.