Useful linux command-line programs

I am a huge fan and enthusiastic of Linux. This is not exclusively due to the fact that it is free, ‘‘free speech, not free beer’’. Its strong terminal-based commands appear to be a great opportunity to perform repetitive tasks very easily with little knowledge of bash. As I am into academia, I will show useful command-line programs to facilitate academic-related tasks. Nonetheless, all code shown here can be easily used and/or adapted for other tasks.

Convert images

A frequent task is to convert a set of images from one file extension to another. A very powerful program to perform this is ImageMagick. As stated on its website, “ImageMagick® is a free, open-source software suite, used for editing and manipulating digital images. It can be used to create, edit, compose, or convert bitmap images, and supports a wide range of file formats, including JPEG, PNG, GIF, TIFF, and PDF.”

For those running a Debian-based distribution (another reason I love Linux)

sudo apt install imagemagick

is all that is needed to install ImageMagick (and most other programs). The program convert is a member of ImageMagick suite and, it is the program used to convert images from one file extension to another. Let us consider a folder containing .png images.

.
├── 1.png
├── 2.png
├── 3.png
├── 4.png
└── 5.png

To convert all of them to .jpg at once, for instance, simply open a terminal, navigate to the folder containing the images, and enter the following command:

ls -1 *.png | parallel convert '{}' '{.}.jpg'

The code above firstly lists all filenames, with one filename per line, having the .png extension. Them the result is ‘‘piped’’ to parallel using | operator, that runs convert in parallel to convert all files to .jpg. parallel will be explained in a future opportunity. In the current folder, you will see both .png and .jpg images. If you want to remove all .png file, simply run

rm *.png 

Certainly, the same procedure can be done for other file formats. To obtain a complete list of supported file formats, run:

convert identify -list format 

In addition to simple image conversion, convert offers other options for editing, such as 3-D effects and color changes. Consulting the manual is always a worthwhile action. You can quickly access it by running man. For instance,

man convert

In summary, to convert a set of files from one file format to another and remove the files of the original format, use the following command:

ls -1 *.png | parallel convert '{}' '{.}.jpg' && rm *.png

In this context, the && command function as and, meaning that it runs the first command and them the second one.

The text you provided is well-written and generally free of major grammar errors. However, there are a few minor improvements that could be made for clarity and consistency:

Join PDF Files

It is not rare to need to join a bunch of .pdf files into a single file. Recently, I was asked to upload PDF files containing all required documents as a single document. Like many tasks, there are several ways to accomplish this. For instance, you can use websites such as iLovePDF, Adobe, or Foxit. Alternatively, you can use software applications, some of which may be paid and come with unnecessary features. One drawback of using web-based services is privacy concerns: you may not know where these files will be uploaded. Another issue, although not a problem for everyone, is the requirement to manually select files for uploading to the website or software. An easy solution is to use pdfunite from the Poppler toolkit.

On a Debian-based system, you can install Poppler as follows:

sudo apt install poppler-utils

Let’s consider the following folder containing the files to be combined, sorted in numerical order for the desired output merged file:

.
├── 1.pdf
├── 2.pdf
├── 3.pdf
├── 4.pdf
├── 5.pdf
├── 6.pdf
├── 7.pdf
├── 8.pdf
└── 9.pdf

Similar to the commands shown earlier:

pdfunite *.pdf output.pdf

With this command, pdfunite combines all .pdf files and saves them as output.pdf (you can choose any filename other than “output”). After entering ls -1 in the current folder, you will see:

.
├── 1.pdf
├── 2.pdf
├── 3.pdf
├── 4.pdf
├── 5.pdf
├── 6.pdf
├── 7.pdf
├── 8.pdf
├── 9.pdf
└── output.pdf