When porting Unix utilities to iOS (vim, TeX, python...), sometimes the source code executes system commands, using
system() calls. These calls are rejected at compile time, with:
error: 'system' is unavailable: not available on iOS.
This project provides a drop-in replacement for
system(). Simply add the following lines at the beginning of you header file:
extern int ios_system(char* cmd); #define system ios_system
link with the
ios_system.framework, and your calls to
system() will be handled by this framework.
Commands available: shell commands (
rm...), archive commands (
compress...) plus a few interpreted languages (
TeX). Scripts written in one of the interpreted languages are also executed, if they are in the
The commands available are defined in two dictionaries,
Resources/extraCommandsDictionary.plist. At startup time,
ios_system loads these dictionaries and enables the commands defined inside. You will need to add these two dictionaries to the "Copy Bundle Resources" step in your Xcode project.
Each command is defined inside a framework. The framework is loaded when the command is called, and released after the command exits. Frameworks for small commands are in this project. Frameworks for interpreted languages are larger, and available separately: python, lua and TeX.
Network-based commands (nslookup, dig, host, ping, telnet) are also available as a separate framework, network_ios. Place the compiled library with the other libraries and add it to the embedded libraries of your application.
ios_system framework has been successfully integrated into four shells, Blink, OpenTerm, Pisth and LibTerm, an editor, iVim and a TeX-writing app, TeXable. Each time, it provides a Unix look-and-feel (well, mostly feel).
Issues: In iOS, you cannot write in the
~ directory, only in
~/tmp. Most Unix programs assume the configuration files are in
So either you redefine
~/Documents/ or you set configuration variables (using
setenv) to some other place. This is done in the
Here's what I have:
setenv PATH = $PATH:~/Library/bin:~/Documents/bin setenv PYTHONHOME = $HOME/Library/ setenv SSH_HOME = $HOME/Documents/ setenv CURL_HOME = $HOME/Documents/ setenv HGRCPATH = $HOME/Documents/.hgrc/ setenv SSL_CERT_FILE = $HOME/Documents/cacert.pem
Your Mileage May Vary. Note that iOS already defines
The easy way: (Xcode 12 and above)
ios_system is available as a set of binary frameworks. Add this project as "Swift Package dependency", and link and embed the frameworks as you need them.
The semi-hard way:
swift run --package-path xcfs build. This will download all the requirements (
openssl) and build all the ios_system XcFrameworks, in the
The hard way:
ios_system.xcodeprojand hit build. This will create the
ios_systemframework, ready to be included in your own projects.
ssh_cmd. This will create the corresponding frameworks.
xcodebuild -project ios_system.xcodeproj -alltargets -sdk iphoneos -configuration Release -quietto build all the frameworks.
ios_systemframework to compile.
libtar.dylibif you need
libfiles.dylibfor cp, rm, mv...).
Resources/extraCommandsDictionary.plistto the "Copy Bundle Resources" step in your Xcode project.
The simplest way to integrate
ios_system into your app is to just replace all calls to
system() with calls to
ios_system(). If you need more control and information, the following functions are available:
initializeEnvironment()sets environment variables to sensible defaults.
ios_executable(char* inputCmd)returns true if
inputCmdis one of the commands defined inside
NSArray* commandsAsArray()returns an array with all the commands available, if you need them for helping users.
NSString* commandsAsString()same, but with a
NSString* getoptString(NSString* command)returns a string containing all accepted flags for a given command ("dfiPRrvW" for "rm", for example). Letters are followed by ":" if the flag cannot be combined with others.
NSString* operatesOn(NSString* command)tells you what this command expects as arguments, so you can auto-complete accordingly. Return values are "file", "directory" or "no". For example, "cd" returns "directory".
int ios_setMiniRoot(NSString* mRoot)lets you set the sandbox directory, so users are not exposed to files outside the sandbox. The argument is the path to a directory. It will not be possible to
cdto directories above this one. Returns 1 if succesful, 0 if not.
FILE* ios_popen(const char* inputCmd, const char* type)opens a pipe between the current command and
inputCmd. (drop-in replacement for
replaceCommand(NSString* commandName, int (*newFunction)(int argc, char *argv), bool allOccurences) lets you replace an existing command implementation with your own, or add new commands without editing the source.
replaceCommand(@"ls", gnu_ls_main, true);: Replaces all calls to
ls to calls to
gnu_ls_main. The last argument tells whether you want to replace only the function associated with
false) or all the commands that used the function previously associated with
ls(if true). For example,
uncompress are both done with the same function,
compress_main (and the actual behaviour depends on
argv). Only you can know whether your replacement function handles both roles, or only one of them.
If the command does not already exist, your command is simply added to the list.
NSError* addCommandList(NSString* fileLocation) loads several commands at once, and adds them to the list of existing commands.
fileLocation points to a plist file, with the same syntax as
Resources/extraCommandsDictionary.plist: the key is the command name, and is followed by an Array of 4 Strings: name of the framework, name of the function to call, list of options (in
getopt() format) and what the command expects as argument (file, directory, nothing). The last two can be used for autocomplete. The name of the framework can be
MAIN if your command is defined in your main program (equivalent to the
RTLD_MAIN_ONLY option for
SELF if it is defined inside
ios_system.framework (equivalent to
<key>rlogin</key> <array> <string>network_ios.framework/network_ios</string> <string>rlogin_main</string> <string>468EKLNS:X:acde:fFk:l:n:rs:uxy</string> <string>no</string> </array>
ios_execv(const char path, char const argv): executes the command in
argv with the arguments
argv (it doesn't use
path). It is not a drop-in replacement for
execv because it does not terminate the current process.
execv is usually called after
execv terminates the child process. This is not possible in iOS. If
dup2 was called before
execv to set stdin and stdout,
ios_execv tries to do the right thing and pass these streams to the process started by
ios_execve also exists, and stores the environment.
ios_system is OpenSource; you can extend it in any way you want. Keep in mind the intrinsic limitations:
traceroute) are impossible.
To add a command:
ios_system.framework; this will replace most function calls by
isatty()with calls to
ios_system, standard output must go to
libc_replacement.cintercepts most of the output functions, but not all.
__thread, make sure local variables are marked with
access... (some of these fail at compile time, others fail silently at run time).
Resources/extraCommandsDictionary.plistto add your command, and run.
Frequently asked commands: here is a list of commands that are often requested, and my experience with them:
telnet: now provided in the network_ios package.
tracerouteand most network analysis tools: require root privilege, so impossible inside a sandbox.
zsh: shells are hard to compile, even without the sandbox/API limitations. They also tend to take a lot of memory, which is a limited asset.
git: WorkingCopy does it very well, and you can transfer directories to your app, then transfer back to WorkingCopy. Also difficult to compile.
ios_system itself is released under the Revised BSD License (3-clause BSD license). Foe the other tools, I've used the BSD version as often as possible:
Using BSD versions has consequences on the flags and how they work. For example, there are two versions of
sed, the BSD version and the GNU version. They have roughly the same behaviour, but differ on
-i (in place): the GNU version overwrites the file if you don't provide an extension, the BSD version won't work unless you provide the extension to use on the backup file (and will backup the input file with that extension).
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