A Shell - IOS Terminal Overview
What is A Shell - IOS Terminal?
a-shell: A terminal for iOS, with multiple windows
The goal in this project is to provide a simple Unix-like terminal on iOS. It uses ios_system for command interpretation, and will ultimately include all commands from the ios_system ecosystem (nslookup, whois, python3, lua, pdflatex, lualatex...) The project uses iPadOS 13 ability to create and manage multiple windows. Each window has its own context, appearance, command history and current directory. newWindow opens a new window, exit closes the current window. For help, type help in the command line. help -l lists all the available commands. help -l | grep command will tell you if your favorite command is already installed. You can change the appearance of a-Shell using config. It lets you change the font, the font size, the background color, the text color and the cursor color. Each window can have its own appearance. config -p will make the settings for the current window permanent, that is used for all future windows. When opening a new window, a-Shell executes the file .profile if it exists. You can use this mechanism to customize further, e.g. have custom environment variables or cleanup temporary files.
a-Shell is now available on the AppStore.
In iOS, you cannot write in the ~ directory, only in ~/Documents/, ~/Library/ and ~/tmp. Most Unix programs assume the configuration files are in $HOME. So a-Shell changes several environment variables so that they point to ~/Documents. Type env to see them. Most configuration files (Python packages, TeX files, Clang SDK...) are in ~/Library.
Sandbox and Bookmarks
a-Shell uses iOS 13 ability to access directories in other Apps sandbox. Type pickFolder to access a directory inside another App. Once you have selected a directory, you can do pretty much anything you want here, so be careful. All the directories you access with pickFolder are bookmarked, so you can return to them later without pickFolder. You can also bookmark the current directory with bookmark. showmarks will list all the existing bookmarks, jump mark will change the current directory to this specific bookmark, renamemark will let you change the name of a specific bookmark and deletemark will delete a bookmark. A user-configurable option in Settings lets you use the commands s, g, l, r and d instead or as well. If you are lost, cd will always bring you back to ~/Documents/. cd - will change to the previous directory.
a-Shell is compatible with Apple Shortcuts, giving users full control of the Shell. You can write complex Shortcuts to download, process and release files using a-Shell commands. There are three shortcuts: Shortcuts can be executed either "In Extension" or "In App". "In Extension" means the shortcut runs in a lightweight version of the App, without no graphical user interface. It is good for light commands that do not require configuration files or system libraries (mkdir, nslookup, whois, touch, cat, echo...). "In App" opens the main application to execute the shortcut. It has access to all the commands, but will take longer. Once a shortcut has opened the App, you can return to the Shortcuts app by calling the command open shortcuts://. The default behaviour is to try to run the commands "in Extension" as much as possible, based on the content of the commands. You can force a specific shortcut to run "in App" or "in Extension", with the warning that it won't always work. Both kind of shortcuts run by default in the same specific directory, $SHORTCUTS. Of course, since you can run the commands cd and jump in a shortcut, you can pretty much go anywhere.
Programming / add more commands:
a-Shell has several programming languages installed: Python, Lua, JS, C, C++ and TeX. For C and C++, you compile your programs with clang program.c and it produces a webAssembly file. You can then execute it with wasm a.out. You can also link multiple object files together, make a static library with ar, etc. Once you are satisfied with your program, if you move it to a directory in the $PATH (e.g. ~/Documents/bin) and rename it program.wasm, it will be executed if you type program on the command line. You can also cross-compile programs on your main computer using our specific WASI-sdk, and transfer the WebAssembly file to your iPad or iPhone. Precompiled WebAssembly commands specific for a-Shell are available here: https://github.com/holzschu/a-Shell-commands These include zip, unzip, xz, ffmpeg... You install them on your iPad by downloading them and placing them in the $PATH. We have the limitations of WebAssembly: no sockets, no forks, no interactive user input (piping input from other commands with command | wasm program.wasm works fine). For Python, you can install more packages with pip install packagename, but only if they are pure Python. The C compiler is not yet able to produce dynamic libraries that could be used by Python. TeX files are not installed by default. Type any TeX command and the system will prompt you to download them. Same with LuaTeX files.
If you enable VoiceOver in Settings, a-Shell will work with VoiceOver: reading commands as you type them, reading the result, letting you read the screen with your finger...
Course Category: Mobile Development
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