My tale of woe
When I started to write my first ebook I decided to use pandoc to transform markdown into pdf.
It basically looked like this
pandoc metadata_de.yaml -o ./level_up_de.pdf --from markdown -V lang=de-DE level_up_de.md
This simple command can be pasted into the command line everytime I want to build a new version of the ebook.
But: I have to keep in mind the command which is tedious. I could write it into a text file and copy it everytime I use it.
There is a more elegant way: let’s make a script!
Make a script
A shell script is basically a file with the extension “.sh”
When You want to specify which shell shall be used, you put
#!/bin/bash
in the first line of your script.
Echo
To put some text on the command line for e.g. displaying the start of your script, you can use the command echo like this
echo "Start generating PDF"
The script now looks like that
#!/bin/bash
echo "Start generating PDF"
pandoc metadata_de.yaml -o ./level_up_de.pdf --from markdown -V lang=de-DE level_up_de.md
Variables
After finishing the German version I also wanted to create an English version,
so the “de” strings should be replaced by a variable to switch between languages.
To declare a variable, you write down the name and assign it a value with the equal sign.
You use a variable by using thew $ sign to access its content.
language="en"
echo "Language: $language"
Caveat: whitespaces are not allowed around the equal sign!
language = "en" # this won't work
Let’s have a look at our script now:
#!/bin/bash
echo "Start generating PDF"
lang="en"
echo "Language: $lang"
pandoc metadata_$lang.yaml -o ./level_up_$lang.pdf --from markdown -V lang=de-DE level_up_$lang.md
Pretty neat!
But we need to get rid of the “de-DE” as well
Conditions
When we get “en” as language we want to use en-US as language subtag. When “de” is used we want de-DE
Let’s write some conditions.
if [[ $lang = "en" ]]
then
lang_subtag="$lang-US"
elif [[ $lang = "de" ]]
then
lang_subtag="$lang-DE"
else
echo "Wrong language"
fi
Now we can replace the de-DE with $lang_subtag
pandoc metadata_$lang.yaml -o ./level_up_$lang.pdf --from markdown -V lang=$lang_subtag level_up_$lang.md
Command Line Arguments
Now that we can generate the ebook for english and german we could introduce a command line parameter.
In bash every argument provided to the script is stored in variables $1 .. $n
lang="$1"
Arrays and loops
I wanted to break down the big markdown file into individual chapters.
To make an array variable in bash you can do the following:
chapters=(
./de/chapter_01.txt
./de/chapter_02.txt
./de/chapter_03.txt
)
Looping over an array looks like this:
for chapter in ${chapters[*]}
do
cat "$chapter"
printf "\n"
done
So now we can pass the chapters array to pandoc
pandoc metadata_$lang.yaml -o ./level_up_$lang.pdf --from markdown -V lang=$lang_subtag ${chapters[*]}
To be continued …
You can find the source code here: https://github.com/jboegeholz/shell_tutorial
