Reloading .bashrc within a BASH terminal session

BASH is a command-line interpretor that is commonly used by Linux and UNIX operating systems. Chances are that you will find find yourself in a BASH session if you start up a terminal emulator in many of these though there are others like KSH and SSH too.

BASH comes with its own configuration files and one of these is located in your own home directory, .bashrc. Among other things, it can become a place to store command shortcuts or aliases. Here is an example:

alias us=’sudo apt-get update && sudo apt-get upgrade’

Such a definition needs there to be no spaces around the equals sign and the actual command to be declared in single quotes. Doing anything other than this will not work as I have found. Also, there are times when you want to update or add one of these and use it without shutting down a terminal emulator and restarting it.

To reload the .bashrc file to use the updates contained in there, one of the following commands can be issued:

source ~/.bashrc

. ~/.bashrc

Both will read the file and execute its contents so you get those updates made available so you can continue what you are doing. There appears to be a tendency for this kind of thing in the world of Linux and UNIX because it also applies to remounting drives after a change to /etc/fstab and restarting system services like Apache, MySQL or Nginx. The command for the former is below:

sudo mount -a

Often, the means for applying the sorts of in-situ changes that you make are simple ones too and anything that avoids system reboots has to be good since you have less work interruptions.

Copying only updated new or updated files by command line in Linux or Windows

With a growing collection of photographic images, I often find myself making backups of files using copy commands and the data volumes are such that I don’t want to keep copying the same files over and over again so incremental file transfers are what I need. So commands like the following often get issued from a Linux command line:

cp -pruv [source] [destination]

Because this is in Linux, it the bash shell that I use so the switches may not apply to others like ssh, fish or ksh. For my case, p preserves file properties such as its time and date and the cp command does not do this always so it needs adding. The r switch is useful because the copy then in recursive so only a directory needs to specified as the source and the destination needs to be one level up from a folder with the same name there so as to avoid file duplication. It is the u switch that makes the file copy incremental and the v one issues messages to the shell that show how the copying is going. Seeing a file name issued by the latter does tell you how much more needs to be copied and that the files are going where they should.

What inspired this post though is my need to do the same in a Windows session and issuing xcopy commands will achieve the same end. Here are two that will do the needful:

xcopy [source] [destination] /d /s

xcopy [source] [destination] /d /e

In both cases, it is the d switch that ensures that the copy is incremental and you can add a date too, with a colon between it and the /d, if you see fit. The s switch copies only directories that contain files while the e one copies even empty directories. Using the d switch without either of those did not trigger any copying action when I tried so I reckon that you cannot do without either of them. By default, both of these commands issue output to the command line so you can keep an eye on what is happening and this especially is useful when ensuring that files are going to the right destination because the behaviour differs from that of the bash shell in Linux.

ImageMagick and Ubuntu 9.04

Using a command line tool like ImageMagick for image processing may sound a really counter-intuitive thing to do but there’s no need to do everything on a case by case interactive basis. Image resizing and format conversion come to mind here. Helper programs are used behind the scenes too with Ghostscript being used to create Postscript files, for example.

The subject of helper programs brings me to an issue that has hampered me recently. While I am aware that there are tools like F-Spot available, I am also wont to use a combination of shell scripting (BASH & KSH), Perl and ImageMagick for organising my digital photos. My preference for using Raw camera files (DNG & CRW) means that ImageMagick cannot access these without a little helper. In the case of Ubuntu, it’s UFRaw. However, Jaunty Jackalope appears to have seen UFRaw updated to a version that is incompatible with the included version of ImageMagick (6.4.5 as opposed to 3.5.2 at the time of writing). The result is that the command issued by ImageMagick to UFRaw -- issue the command man ufraw-batch to see the details -- is not accepted by the included version of the latter, 0.15 if you’re interested. It seems that an older release of UFRaw accepted the output device ppm16 (16-bit PPM files) but this should now be specified as ppm for the output device and 16 for the output depth. In a nutshell, where the parameter output-type did the lot, you now need both output-type and output-depth.

I thought of decoupling things by using UFRaw to create 16-bit PPM files for processing by ImageMagick but to no avail. The identify command wouldn’t return the date on which the image was taken. I even changed the type to 8-bit JPEG’s with added EXIF information but no progress was made. In the end, a mad plan came to mind: creating a VirtualBox VM running Debian. The logic was that if Debian deserves its reputation for solidity, dependencies like ImageMagick and UFRaw shouldn’t be broken and I wasn’t wrong. To make it fly though, I needed to see if I could get Guest Additions installed on Debian. Out of the box, the supported kernel version must be at least 2.6.27 and Debian’s is 2.6.26 so additional work was on the cards. First, GCC, Make and the correct kernel header files need to be installed. Once those are in place, the installation works smoothly and a restart sets the goodies in motion. To make the necessary Shared folder to be available, a command like the following was executed:

mount -t vboxfs [Shared Folder name] [mount point]

Once that deed was done and ImageMagick instated, the processing that I have been doing for new DSLR images was reinstated. Ironically, Debian’s version of ImageMagick, 6.3.7, is even older than Ubuntu’s but it works and that’s the main thing. There is an Ubuntu bug report for this on Launchpad so I hope that it gets fixed at some point in the near future. However, that may mean awaiting 9.10 or Karmic Koala so I’m glad to have the workaround in the meantime.