∙ Editing files
How to create and modify files
Text editors
We can create and modify files on the command line using text editors. These are like very minimal word-processors, with no formatting options, but with many powerful ways of editing that are not available in word-processors. There are lots of different command line editors, which range from user-friendly (but less powerful), to more difficult (but powerful and fast, once learned).
Here are some common editors you might come across, or choose to learn:
nanoan easy to use and widely-available editormicroa more modern version of nanoemacsa hugely-powerful editor, jokingly referred to as an operating system in itself. Medium learning-curve.jovea minimal version of emacs (this is my favourite ;)vimis legendary as the “coder’s editor”, being very powerful, very fast, but having a steep learning curve and heavy reliance on keyboard shortcuts. Very widely available - almost all systems haveviminstalled.
Editing a file with nano
We will learn the basics with nano. Run this command:
nano animals.txt
The screen will look a little different: just like with less, you are now not on the command line, but running the program called nano. Try making some changes to the file with your keyboard (remember the mouse cannot move your cursor).
There are many commands that nano can do, but here are a few you will need to know
ctrl-ois save (“output a file”)ctrl-wis search (“where?”)ctrl-xis used to exitnano.
Note that there is a basic cheatsheet along the bottom of the screen for some common commands inside nano.
Creating a new file
Have a play. Exit back to the command line. Now we are going to make a new file. You can call it whatever you like - as long as that file name doesn’t already exist here, it will make an empty file.
nano my_new_file
Note that in Linux systems and MacOS, the file extensions (for example .txt or .mp3 or .pdf) are entirely optional. You can even have multiple extensions, like file.txt.new.extension, which to Linux system is all just the name. In Windows, file extensions are important! They are also useful for humans too, so where it is appropriate, best to stick to convention. Calling an .mp3 file a .docx file is valid, but highly confusing :)
If you try to leave nano (ctrl-x) when there are unsaved changes, it will ask to save modified buffer?. So, save or not with y or n, and let’s look at examining files back on the command line. (A “buffer” is information that exists on your screen, or in your RAM, but does not exist in storage memory. In other words, stuff you have not saved yet.)
Don’t be afraid of error messages :)
When you get things wrong, the command line will tell you, but messages can seem hard to understand. Most commonly, the message will tell you what went wrong, or how to use a command. For example, if I try to copy a file which does not exist:
cp file99999 file3
the computer responds with
cp: file99999: No such file or directory
Think of this as a speech bubble, with cp: being who is speaking, here saying that a file doesn’t exist, at least not in this folder. Here is another example
lf
and the shell itself (zsh in this case) tells you it doesn’t know what lf means:
zsh: command not found: lf
Some commands will give you very brief instructions on how it is used as an error message. For example, if we ask mv to run, but not actually move anything,
mv
we get a couple of usage instructions:
usage: mv [-f | -i | -n] [-v] source target
mv [-f | -i | -n] [-v] source ... directory
The items in the square brackets are flags that mv can take, and source target tells you the order of arguments. The ... means that you can copy multiple items to a single target location (typically, when you mv multiple items into the same folder).