Technology Tales

Accessing Julia REPL command history

In the BASH shell used on Linux and UNIX, the history command calls up a list of recent commands used and has many uses. There is a .bash_history file in the root of the user folder that logs and provides all this information so there are times when you need to exclude some commands from there but that is another story.

The Julia REPL environment works similarly to many operating system command line interfaces, so I wondered if there was a way to recall or refer to the history of commands issued. So far, I have not come across an equivalent to the BASH history command for the REPL itself but there the command history is retained in a file like .bash_history. The location varies on different operating systems though. On Linux, it is ~/.julia/logs/repl_history.jl while it is %USERPROFILE%\.julia\logs\repl_history.jl on Windows. While I tend to use scripts that I have written in VSCode rather than entering pieces of code in the REPL, the history retains its uses and I am sharing it here for others. In the past, the location changed but these are the ones with Julia 1.8.2, the version that I have at the time of writing.

Restoring the menu bar on GNOME Terminal in a GNOME Shell session

By default, a GNOME Terminal instance does not display a menu bar and that applies not only in GNOME Shell but also on the Cinnamon Desktop environment. In the latter, it is easy enough to display the menu bar using the context menu produced by right clicking in the window before going to Edit > Preferences and ticking the box for Show menubar by default in new terminals in the General section. After closing the Preferences dialogue, every new GNOME Terminal session will show the menu bar.

Unfortunately, it is not so easy in GNOME Shell though the context menu route does allow you to unhide the menu bar on a temporary basis. That is because the requisite tickbox is missing from the Preferences dialogue box displayed after navigating to Edit > Preferences in the menus. To address, you need the execute the following command in a terminal session:

gsettings set org.gnome.Terminal.Legacy.Settings headerbar false

This not only adds the menu bar on a permanent basis but it also adds the missing tickbox, populated as required. GNOME Shell may be minimalist in some ways but making this action harder looks like going a little too far.

Installing Perl modules using CPAN on Linux Mint 19.2

My online travel photo gallery is a self-coded set of PHP scripts that read data from tables in a MySQL database. These tables are built from input XML files using a Perl script that itself creates and executes an SQL script. The Perl script also does some image processing using GraphicsMagick commands to resize images and to add copyright information and image framing. Because this processed one image at a time sequentially, it was taking several minutes to complete and only partly used the capacity of the PC that I used.

This led me to look at adding parallel processing and that is what brought me to looking at the Parallel::ForkManager Perl module. An alternative approach might have been to add new images in such a way as not to need the full run involving hundreds of image files, but that will take more work and I fancied having a look at parallelising things anyway.

If it was not there already, the first act would have been to install build-essential to get access to the cpan command. The following command accomplishes this:

sudo apt-get install build-essential

Once that is there, the cpan command needs to be run and some questions answered to get things going. The first question to answer is whether you want setup to be as automated as possible and the default answer of yes worked for me. The next question to answer regards the approach that cpan takes when installing modules and I chose sudo here (local::lib is the default value and manual is another option). After this, cpan drops into its own command shell. Here, I issued two more commands to continue the basic setup by updating CPAN.pm to the latest version and adding Bundle::CPAN to optimise the module further:

make install
install Bundle::CPAN

Continuing the last of these may need extra intervention to confirmation the suggested default of exit at one point in its operation and that takes a little time to complete. It is after this that Parallel::ForkManager can be installed using the following command:

install Parallel::ForkManager

That completed quickly and the cpan shell was exited using its exit command. Then, the new module was available in scripting after that. The actual use of this module is something that hope to describe in another post so I am ending this one here and the same process is just as applicable to setting up cpan and adding any other Perl CPAN module.

Changing file timestamps using Windows PowerShell

Recently, a timestamp got changed on an otherwise unaltered file on me and I needed to change it back. Luckily, I found an answer on the web that used PowerShell to do what I needed and I am recording it here for future reference. The possible commands are below:

$(Get-Item temp.txt).creationtime=$(Get-Date "27/10/2014 04:20 pm")
$(Get-Item temp.txt).lastwritetime=$(Get-Date "27/10/2014 04:20 pm")
$(Get-Item temp.txt).lastaccesstime=$(Get-Date "27/10/2014 04:20 pm")

The first of these did not interest me since I wanted to leave the file creation date as it was. The last write and access times were another matter because these needed altering. The Get-Item commandlet brings up the file, so its properties can be set. Here, these include creationtime, lastwritetime and lastaccesstime. The Get-Date commandlet reads in the provided date and time for use in the timestamp assignment. While PowerShell itself is case-insensitive, I have opted to show the camel case that is produced when you are tabbing through command options for the sake of clarity.

The Get-Item and Get-Date have aliases of gi and gd, respectively and the Get-Alias commandlet will show you a full list while Get-Command (gcm) gives you a list of commandlets. Issuing the following gets you a formatted list that is sent to a text file:

gcm | Format-List > temp2.txt

There is some online help but it is not quite as helpful as it ought to be so I have popped over to Microsoft Learn whenever I needed extra enlightenment. Here is a command that pops the full thing into a text file:

Get-Help Format-List -full > temp3.txt

In fact, getting a book might be the best way to find your way around PowerShell because of all its commandlets and available objects.

For now, other commands that I have found useful include the following:

Get-Service | Format-List
New-Item -Name test.txt -ItemType "file"

The first of these gets you a list of services while the second creates a new blank text file for you and it can create new folders for you too. Other useful commandlets are below:

Get-Location (gl)
Set-Location (sl)
Copy-Item
Remove-Item
Move-Item
Rename-Item

The first of the above is like the cwd or pwd commands that you may have seen elsewhere in that the current directory location is given. Then, the second will change your directory location for you. After that, there are commandlets for copying, deleting, moving and renaming files. These also have aliases so users of the legacy Windows command line or a UNIX or Linux shell can use something that is familiar to them.

Little fixes like the one with which I started this piece are all very good to know but it is in scripting that PowerShell really is said to show its uses. Having seen the usefulness of such things in the world on Linux and UNIX, I cannot disagree with that and PowerShell has its own IDE too. That may be just as well given how much there is to learn. That especially is the case when you might need to issue the following command in a PowerShell session opened using the Run as Administrator option just to get the execution as you need it:

Set-ExecutionPolicy RemoteSigned

Issuing Get-ExecutionPolicy will show you if this is needed when the response is: Restricted. A response of RemoteSigned shows you that all is in order, though you need to check that any script you then run has no nasty payload in there, which is why execution is restrictive in the first place. This sort of thing is yet another lesson to be learnt with PowerShell.

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.

Fixing Background Image Display in GNOME Shell 3.10

On upgrading from Ubuntu GNOME 13.10 to Ubuntu GNOME 14.04, a few rough edges were to be noticed. One was the display of my chosen background image: it was garbled. Later, I discovered that there is a maximum width of 2560 px for background images in GNOME Shell these days and that things get messy beyond that.

In my case, the image width was around 6000 px and I was used to its getting resized in GNOME Shell 3.8 and its predecessors. It seems that the functionality got removed after that though so the workaround of manual image resizing in the GIMP needed to be employed. Though having big images open in memory creates an additional overhead, not handling them very well at all looks like a bug caused by setting 2560 px as a maximum screen width for the GNOME Shell panel and the complete removal of Nautilus from desktop rendering duties. Let’s hope that sense is seen with ever larger screen sizes and resolutions coming our way.

It’s the sort of thing that did get me looking at adding on Cinnamon 2.2 for a while before setting background image scaling using the indispensable GNOME Tweak Tool was discovered. LinuxG.net has a useful tutorial on this for anyone with such an adventurous streak in them. For now though, I am OK with my set up but the GNOME project’s focus on minimalism could affect us in other ways so I can see why Clem Lefebvre started the Cinnamon one primarily for Linux Mint and the desktop environment is appearing elsewhere too. After all, Gedit lost its menu bar in GNOME 3.12 so it’s just as well that we have alternative choices.

Update 2014-05-06: It seems that the desktop image bug that afflicts GNOME Shell 3.10 got sorted for GNOME Shell 3.12. At least, that is the impression that an Antergos instance in a VirtualBox virtual machine gives me.

A fallback method of installing Nightingale in Linux

When I upgraded to Ubuntu GNOME 13.10 and went for the 64-bit variant, I tried a previously tried and tested approach for installing Nightingale that used a PPA only for it not to work. At that point, the repository had not caught up with the latest Ubuntu release (it has by the time of writing) and other pre-compiled packages would not work either. However, there was one further possibility left and that was downloading a copy of the source code and compiling that. My previous experiences of doing that kind of thing have not been universally positive so it was not my first choice but I gave it a go anyway.

In order to get the source code, I first needed to install Git so I could take a copy from the version controlled repository and the following command added the tool and all its dependencies:

sudo apt-get install git autoconf g++ libgtk2.0-dev libdbus-glib-1-dev libtag1-dev libgstreamer-plugins-base0.10-dev zip unzip

With that lot installed, it was time to checkout a copy of the latest source code and I went with the following:

git clone https://github.com/nightingale-media-player/nightingale-hacking.git

The next step was to go into the nightingale-hacking sub-folder and issue the following command:

./build.sh

That should produce a sub-directory named nightingale that contains the compiled executable files. If this exists, it can be copied into /opt. If not, then create a folder named nightingale under /opt using copy the files from ~/nightingale-hacking/compiled/dist into that location. Ubuntu GNOME 13.10 comes with GNOME Shell 3.8, the next step took a little fiddling before it was sorted: adding an icon to application menu or dashboard. This involved adding a file called nightingale.desktop in /usr/share/applications/ with the following contents:

[Desktop Entry]
Name=Nightingale
Comment=Play music
TryExec=/opt/nightingale/nightingale
Exec=/opt/nightingale/nightingale
Icon=/usr/share/pixmaps/nightingale.xpm
Type=Application
X-GNOME-DocPath=nightingale/index.html
X-GNOME-Bugzilla-Bugzilla=Nightingale
X-GNOME-Bugzilla-Product=nightingale
X-GNOME-Bugzilla-Component=BugBuddyBugs
X-GNOME-Bugzilla-Version=1.1.2
Categories=GNOME;Audio;Music;Player;AudioVideo;
StartupNotify=true
OnlyShowIn=GNOME;Unity;
Keywords=Run;
Actions=New
X-Ubuntu-Gettext-Domain=nightingale

[Desktop Action New]
Name=Nightingale
Exec=/opt/nightingale/nightingale
OnlyShowIn=Unity

It was created from a copy of another *.desktop file and the categories in there together with the link to the icon were as important as the title and took a little tinkering before all was in place.  Also, you may find that /opt/nightingale/chrome/icons/default/default.xpm needs to be become /usr/share/pixmaps/nightingale.xpm using the cp command before your new menu entry gains an icon to go with it. While the steps that I describe here worked for me, there is more information on the Nightingale wiki if you need it.

Dealing with the Lack of Categories in the Application Overview Screen for GNOME Shell 3.8

One thing that I like to do is peruse the installed applications on any computer system. In most cases, this is simple enough to do but there are some who appear to believe in doing away with that in favour of text box searching. It also seems that the GNOME have fallen into that trap with version 3.8 of GNOME Shell. You could add the Applications Menu extension that is formally part of the GNOME Shell Classic interface and I have done this too. However, that has been known to freeze the desktop session so I am not that big a big fan of it.

However, there is a setting that brings back those application categories in the overview screen and it can be set using dconf-editor. After opening up the application, navigate to org > gnome > shell using the tree in the left hand panel of the tool. Editing the app-folder-categories entry in the right hand panel is what adds the categories back for you. The default is [‘Utilities’, ‘Sundry’] and this needs to be changed to [‘Utilities’, ‘Games’, ‘Sundry’, ‘Office’, ‘Network’, ‘Internet’, ‘Graphics’, ‘Multimedia’, ‘System’, ‘Development’, ‘Accessories’, ‘System Settings’, ‘Other’].

Once the above has been completed, a change is noticeable in that you get a list of categories in the application overview screen and a split of application icons in the middle and categories down the right hand side. Clicking on a category brings up a new panel that contains the application within it and this can be closed again. Cycling through the categories is a process of opening and closing the different panels. The behaviour may be changed but the functionality remains and I have heard that this will be polished further in release 3.10 of GNOME Shell.

For those wanting to to exit all of this and get something like the old GNOME 2, it is possible to add the Classic Session. In Fedora 19, it’s a matter of issuing something like the following command:

sudo yum -y install gnome-classic-session

In reality, this is a case of adding a number of extensions and changing the panel colour from black to grey but it works without needing the category tweak that I described above. The Application Menu extension does need more stability hardening before I’d trust it completely though. There’s no point having a nicer interface if it’s going to freeze up on you too often.

Command Line Processing of EXIF Image Metadata

There is a bill making its way through the U.K. parliament at the moment that could reduce the power of copyright when it comes to images placed on the web. The current situation is that anyone who creates an image automatically holds the copyright for it. However, the new legislation will remove that if it becomes law as it stands. As it happens, the Royal Photographic Society is doing what it can to avoid any changes to what we have now. There may be the barrier of due diligence but how many of us take steps to mark our own intellectual property? For one, I have been less that attentive to this and now wonder if there is anything more that I should be doing. Others may copyleft their images but I don’t want to find myself unable to share my own photos because another party is claiming rights over them. There’s watermarking them but I also want to add something to the image metadata too.

That got me wondering about adding metadata to any images that I post online that assert my status as the copyright holder. It may not be perfect but any action is better than doing nothing at all. Given that I don’t post photos where EXIF metadata is stripped as part of the uploading process, it should be there to see for anyone who bothers to check and there may not be many who do.

Because I also wanted to batch process images, I looked for a command line tool to do the needful and found ExifTool. Being a Perl library, it is cross-platform so you can use it on Linux, Windows and even OS X. To install it on a Debian or Ubuntu based Linux distro, just use the following command:

sudo apt-get install libimage-exiftool-perl

The form of the command that I found useful for adding the actual copyright information is below:

exiftool -p “-copyright=(c) John …” -ext jpg -overwrite_original

The -p switch preserves the timestamp of the image file while the -overwrite_original one ensures that you don’t end up with unwanted backup files. The copyright message goes within the quotes along with the -copyright option. With a little shell scripting, you can traverse a directory structure and change the metadata for any image files contained in different sub-folders. If you wish to do more than this, there’s always the user documentation to be consulted.

A look at Windows 8.1

Last week, Microsoft released a preview of Windows 8.1 and some hailed the return of the Start button but the reality is not as simple as that. Being a Linux user, I am left wondering if ideas have been borrowed from GNOME Shell instead of putting back the Start Menu like it was in Windows 7. What we have got is a smoothing of the interface that is there for those who like to tweak settings and not available be default. GNOME Shell has been controversial too so borrowing from it is not an uncontentious move even if there are people like me who are at home in that kind of interface.

What you get now is more configuration options to go with the new Start button. Right clicking on the latter does get you a menu but this is no Start Menu like we had before. Instead, we get a settings menu with a “Shut down” entry. That’s better than before, which might be saying something about what was done in Windows 8, and it produces a sub-menu with options of shutting down or restarting your PC as well as putting it to sleep. Otherwise, it is place for accessing system configuration items and not your more usual software, not a bad thing but it’s best to be clear about these things. Holding down the Windows key and pressing X will pop up the same menu if you prefer keyboard shortcuts and I have a soft spot for them too.

The real power is to be discovered when you right click on the task bar and select the Properties entry from the pop-up menu. Within the dialogue box box that appears, there is the Navigation tab that contains a whole plethora of interesting options. Corner navigation can be scaled back to remove the options of switching between applications at the upper left corner or getting the charms menu from the upper right corner. Things are interesting in the Start Screen section. This where you tell Windows to boot to the desktop instead of the Start Screen and adjust what the Start button gives you. For instance, you can make it use your desktop background and display the Start Screen Apps View. Both of these make the new Start interface less intrusive and make the Apps View feel not unlike the way GNOME Shell overlays your screen when you hit the Activities button or hover over the upper left corner of the desktop.

It all seems rather more like a series of little concessions and not the restoration that some (many?) would prefer. Classic Shell still works for all those seeking an actual Start Menu and even replaces the restored Microsoft Start button too. So, if the new improvements aren’t enough for you, you still can take matters into your own hands until you start to take advantage of what’s new in 8.1.

Apart from the refusal to give us back a Windows 7 style desktop experience, we now have a touchscreen keyboard button added to the taskbar.So far, it always appears there even when I try turning it off. For me, that’s a bug and it’s something that I’d like to see fixed before the final release.

All in all, Windows 8.1 feels more polished than Windows 8 was and will be a free update when the production version is released. My explorations have taken place within a separate VMware virtual machine because updating a Windows 8 installation to the 8.1 preview is forcing a complete re-installation on yourself later on. There are talks about Windows 9 now but I am left wondering if going for point releases like 8.2, 8.3, etc. might be a better strategy for Microsoft. It still looks as if Windows 8 could do with continual polishing before it gets more acceptable to users. 8.1 is a step forward and more like it may be needed yet.