How to edit file content using zsh terminal? - terminal

Question

I created an empty directory on zsh and added a file
called hello.rb by doing the following:
echo 'Hello, world.' >hello.rb
If I want to make changes in this file using the terminal
what's the proper way of doing it without opening the file
itself using let's say TextEditor?
I want to be able to make changes in the file hello.rb strictly
by using my zsh terminal, is this at all possible?

Answer 1

Zsh is not a terminal but a shell. The terminal is the window in which the shell executes. The shell is the text program prompting you commands and executing them.
If you want to edit the file within the terminal, then using vim, nano, emacs -nw or any other text-mode text editor will do it. They are not Zsh commands, but external commands that you can call from Zsh or from any other shell.
If you want to edit the file within Zsh, then use zed. You will need to run once (in ~/.zshrc)
autoload zed
and then you can edit hello.rb using:
zed hello.rb
(exit and save with Control-j)

Answer 2

You have already created and edited the file.
To edit it again, you can use the >> to append.
For example
echo "\nAnd you too!\n" >> hello.rb
This would edit the file by concatenating the additional string.
Edit, of course, by your use and definition of 'changing' a file, this is the simplest way to do so using the shell.
In a normal way, though you probably want to use a terminal editor.

Answer 3

Zed is a great answer, but to be even more stripped down - for a level of editing that even a script can do - zsh can hand all 256 characters/byte-values (including null) in variables. This means you can edit line by line or chunk by chunk almost any kind of file data directly from the command-line. This is approximately what zed/vared does. If you have a current version with all the standard modules included, it is a great benefit to have zsh/mapfile or zsh/system loaded so that you can capture any of the characters that are left out by command-expansion (zed uses $(<$file) to read a file to memory). Here is an example of a way you could use this variable manipulation method:
% typeset -T Buffer buffer $'\n'
% typeset -T Edit edit $'\n'
It is most common to use newline to divide a text file one wishes to edit.
This handy feature will make zsh give you full access to one line or a range of lines at a time without unintentionally messing with the data.
% zmodload zsh/mapfile
% Buffer=$mapfile[path/to/file]
Here, I use the handy mapfile module because I can load the contents of a file byte-for-byte. Alternately you can use % Buffer="$(<path/to/file)", like zed does, but you will always have the trailing newlines removed and other word splitting is possible with a typo or environment variation, so the simplicity of the module's method is best. When finished, you save the changes by simply assigning the $Buffer value back to the $mapfile[file] or use a more classic command like printf '%s' $Buffer >path/to/file (this is exact string writing, byte-for-byte, so any newlines or formatting you added back will be written).
You transfer the lines between Buffer and Edit using the mapped arrays as follows, however, remember that in its simplest form assigning one array to another drops elements that are completely empty (one \n \n two \n three becomes one \n two \n three). You can suppress this empty-element removal by quoting the input array and adding an '#' symbol to its index "$buffer[#]", if using the whole array; and adding the '#' symbol to the flags if using a range of the array "${(#)buffer[2,50]}". Preserving empty lines can be a bit troublesome for typing, but these multiple arrays should only be used in a script or function, since you can just edit one line at a time from the command line with buffer[54]="echo This is a newly written line."
% edit=($buffer[50,70])
...
% buffer[50,70]=($edit)
This is standard Zsh syntax, that means in the ... area you can edit and manipulate the $edit array of lines or the $Edit scalar block of text all you want, including adding more lines or taking some away. When you add the lines back into $buffer it will replace the specified block of lines (50-70) with the new lines, automatically expanding or reducing the other array elements to accommodate the reintegrated lines. -- Because of the dynamic array accommodations, you can also just insert whatever you need as a new line like this buffer[40]=("new string as new line" "$buffer[40]"). This inserts it before the index given, while swapping the order of the elements ("$buffer[40]" "new string as new line") inserts the new line after the index given. Either will adjust all following elements, including totally empty elements, to their current index plus one.
If you wanted to re-write the zed function to use this method in some complex way like: newzed /path/to/file [start-line] [end-line], that would be great and handy too.
Before I leave, I wanted to mention that using vared directly, once you have these commands typed on the interactive terminal, you may find it frustrating that you can't use "Enter" for inserting or appending new lines. I found that with my terminal and Zsh version using ESC-ENTER worked well, but I don't know about older versions (Mac usually comes stocked with a not-most-recent version, if my memory is right). If that doesn't work, you may have to do some documentation digging to learn how to set up your ZLE (Zsh Line Editor, a component of Zsh) or acquire a newer version of Zsh. Also, some other shells, when indexing a scalar variable may count by the byte because in ascii and C a byte is the same as a character, but Zsh supports UTF8 and will index a scalar string by the UTF8 character unless you turn off the shell option multibyte (on by default). This will help with manipulating each line if you need to use the old byte-character indexing. Also, if you have a version of Zsh that for whatever was not compiled with zsh/mapfile or zsh/system, then you can achieve a similar effect using number of options to the read builtin, like <path/to/file |read -u 0 -k $[5 * 2**20] -r -s Buffer ||(($#Buffer)). As you can see here, you have to make the read length big enough to accommodate the file's size or it will leave off part of the file, and the read return code will nearly always be an error because of not being able to read the full length of the string. We fix this with ||(($#Buffer)), but this builtin was simply not meant to handle large scale byte manipulation efficiently, so what you see is what you can get from it.