GNU Astronomy Utilities


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4.1.3 Shell TAB completion (highly customized)

Under development: Gnuastro’s TAB completion in Bash already greatly improves usage of Gnuastro on the command-line, but still under development and not yet complete. If you are interested to try it out, please go ahead and activate it (as described below), we encourage this. But please have in mind that there are known issues97 and you may find new issues. If you do, please get in touch with us as described in Report a bug. TAB completion is currently only implemented in the following programs: Arithmetic, BuildProgram, ConvertType, Convolve, CosmicCalculator, Crop, Fits and Table. For progress on this task, please see Task 1579998.

Bash provides a built-in feature called programmable completion99 to help increase interactive workflow efficiency and minimize the number of key-strokes and the need to memorize things. It is also known as TAB completion, bash completion, auto-completion, or word completion. Completion is activated by pressing [TAB] while you are typing a command. For file arguments this is the default behavior already and you have probably used it a lot with any command-line program.

Besides this simple/default mode, Bash also enables a high level of customization features for its completion. These features have been extensively used in Gnuastro to improve your work efficiency100. for example, if you are running asttable (which only accepts files containing a table), and you press [TAB], it will only suggest files containing tables. As another example, if an option needs image HDUs within a FITS file, pressing [TAB] will only suggest the image HDUs (and not other possibly existing HDUs that contain tables, or just metadata). Just note that the file name has to be already given on the command-line before reaching such options (that look into the contents of a file).

But TAB completion is not limited to file types or contents. Arguments/Options that take certain fixed string values will directly suggest those strings with TAB, and completely ignore the file structure (for example, spectral line names in Invoking CosmicCalculator)! As another example, the option --numthreads option (to specify the number of threads to use by the program), will find the number of available threads on the system, and suggest the possible numbers with a TAB!

To activate Gnuastro’s custom TAB completion in Bash, you need to put the following line in one of your Bash startup files (for example, ~/.bashrc). If you installed Gnuastro using the steps of Quick start, you should have already done this (the command just after sudo make install). For a list of (and discussion on) Bash startup files and installation directories see Installation directory. Of course, if Gnuastro was installed in a custom location, replace the ‘/usr/local’ part of the line below to the value that was given to --prefix during Gnuastro’s configuration101.

# Enable Gnuastro's TAB completion
source /usr/local/share/gnuastro/completion.bash

After adding the line above in a Bash startup file, TAB completion will always be activated in any new terminal. To see if it has been activated, try it out with asttable [TAB][TAB] and astarithmetic [TAB][TAB] in a directory that contains tables and images. The first will only suggest the files with a table, and the second, only those with an image.

TAB completion only works with long option names: As described above, short options are much more complex to generalize, therefore TAB completion is only available for long options. But do not worry! TAB completion also involves option names, so if you just type --a[TAB][TAB], you will get the list of options that start with an --a. Therefore as a side-effect of TAB completion, your commands will be far more human-readable with minimal key strokes.


Footnotes

(97)

http://savannah.gnu.org/bugs/index.php?group=gnuastro&category_id=128

(98)

https://savannah.gnu.org/task/?15799

(99)

https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion.html

(100)

To learn how Gnuastro implements TAB completion in Bash, see Bash programmable completion.

(101)

In case you do not know the installation directory of Gnuastro on your system, you can find out with this command: which astfits | sed -e"s|/bin/astfits||"


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