Terminal for Plebeians

Not just for nerds, the command line is a great tool for regular people too!

The terminal is oft considered an esoteric tool intended for programmers and none else. The sight of a terminal is immediately associated with coding.

This one time, a classmate asked me after class “What are you always coding?”

I was simply taking lecture notes in vim.

Okay, most would immediately disqualify my being “plebeian” on account of my using vim… doesn’t help that I was writing in markdown.

But this post is more about the terminal being useful in fields other than programming. In this particular case, a university literature course.

The splitting task

The instructor was going to go over excerpts from course material. Some of the material was really long pdf files. But we only needed a few sections. How do we extract out only the parts we need?

We could pay Adobe to let us extract pages. Or my sneaky trick of opening the pdf file in a browser and printing to file after typing in the range of pages I need. But repeating that 12 times with different page ranges each time is meh.

The CLI can split and unite

On the terminal, I have access to a tool called pdfseparate that extracts pages from a pdf. But each page is saved to its own file. Luckily, there’s also a pdfunite that does I could use to combine these files.

But while that solves the question of tools to use, I do still need to repeatedly specify the page numbers somewhat like

pdfseparate -f 4 -l 5 "filename.pdf" "filename-p%d.pdf"
pdfunite "filename-p4.pdf" "filename-p5.pdf" "filename.excerpt.pdf"

That is two separate commands for just one file and each filename and page count needs to be stated so expressly… how is this more efficient?

It isn’t. But the command line offers so much opportunity for efficiency through other features such as loops.

Loops

I could simply change my command to go over all the pdf files and run the commands for each one. By using a variable ${file}, I can let the terminal (technically shell) change the filename for each command.

for file in *.pdf; do
    pdfseparate -f XYZ -l XYZ "${file}.pdf" "${file}-p%d.page" ;
    pdfunite "${file}-p*.page" "${file}.excerpt.pdf" ;
done

Additionally, I set the individual pages to be saved to .page files instead of .pdf file. This lets me use the ${file}-p*.page part to indicate a pattern of filenames instead of specifying each file that needs to be combined by pdfunite; and also won’t interfere with my loop that is looking for the pattern *.pdf.

Wildcards / Globs

The * is called a glob character (or wildcard) to mean that it can match anything. In this particular case, it is being used to select all files whose names match a particular pattern.

Varying page numbers

Yet persists the problem of the required page number ranges being different for each pdf file. I could use variables again. But for this one, a little bit of manual typing is needed. So I created a spreadsheet and pushed off delegated to a classmate, the work of keying in the first and last page number for each filename.

Spreadsheets can be easily exported to CSV (comma-separated value) files. Then, I used a different loop on the CSV file’s rows instead of working on *.pdf as I did before.

filename-093.pdf,5,45
fileplace-02.pdf,3,12
fileanima-98.pdf,9,11
filethgns-09.pdf,1,9

The above is a sample CSV file. Now I could get values for three variables from each row of the file, the filename, first page and last page.

while IFS=, read file firstp lastp; do
    pdfseparate -f ${firstp} -l ${lastp} "${file}.pdf" "${file}-p%d.page" ;
    pdfunite "${file}-p*.page" "${file}.excerpt.pdf" ;
done

You could also go further and combine all the excerpts into a single big file using the handy *.excerpt.pdf pattern.

pdfunite "*.exercpt.pdf" "allmaterial.pdf"

CLI for mooore than just code

And with that I conclude this badly written blog post. The CLI is useful in situations other than coding—such as a university literature course.

Or to simple take notes in class if you use vim 😎