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 (ls
, cp
, rm
...), archive commands (curl
, scp
, sftp
, tar
, gzip
, compress
...) plus a few interpreted languages (python
, lua
, TeX
). Scripts written in one of the interpreted languages are also executed, if they are in the $PATH
.
The commands available are defined in two dictionaries, Resources/commandDictionary.plist
and 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. Some commands (curl
, python
) require OpenSSH
and libssl2
, which you will have to download and compile separately (see https://github.com/holzschu/libssh2-for-iOS, for example).
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.
This ios_system
framework has been successfully ported into two shells, Blink and OpenTerm and into an editor, iVim. Each time, it provides a Unix look-and-feel (well, mostly feel).
Issues: 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 either you redefine $HOME
to ~/Documents/
or you set configuration variables (using setenv
) to some other place. This is done in the initializeEnvironment()
function.
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 $HOME
and $PATH
.
scp
and sftp
are implemented by rewriting them as curl
commands. For example, scp user@host:~/distantfile localfile
becomes (internally) curl scp://user@host/~/distantFile -o localFile
. This was done to keep the size of the framework as small as possible. It will work for most of the users and most of the commands. However, it has consequences:
scp
from distant file to distant file probably won't work, only from local to distant or distant to local.- The flags are those from
curl
, notscp
. Except-q
(quiet) which I remapped to-s
(silent). - The config file is
.curlrc
, not.ssh/config
. - The library used internally is
libssh2
, notOpenSSH
.
The easy way: run the script ./get_binaries.sh
. This will download the compiled versions of all existing frameworks (ios_system.framework
, plus all the frameworks libraries, including network_ios
).
The hard way:
- Run the script
./get_sources.sh
. This will download the latest sources form Apple OpenSource and patch them for compatibility with iOS. - We need libSSH2 and OpenSSL. Either:
- [Fast] Run the script
./get_frameworks.sh
to download precompiled versions ofopenSSL.framework
andlibSSH2.framework
. - [Slow] Run the script
./get_frameworks_as_source.sh
to download the source foropenSSL.framework
andlibSSH2.framework
, compile them, and move them toFrameworks
.
- [Fast] Run the script
- Open the Xcode project
ios_system.xcodeproj
and hit build. This will create theios_system
framework, ready to be included in your own projects. - Compile the other targets as well: files, tar, curl, awk, shell, text, ssh_cmd. This will create the corresponding frameworks.
- Alternatively, type
xcodebuild -project ios_system.xcodeproj -alltargets -sdk iphoneos -configuration Debug -quiet
to build all targets. - If you need python, lua, TeX or network_ios, download the corresponding projects and compile them. All these projects need the
ios_system
framework to compile.
- Link your application with the
ios_system.framework
framework. - Embed (but don't link) the frameworks corresponding to the commands you need (
libtar.dylib
if you needtar
,libfiles.dylib
for cp, rm, mv...). - Add the two dictionaries,
Resources/commandDictionary.plist
andResources/extraCommandsDictionary.plist
to 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 ifinputCmd
is one of the commands defined insideios_system
.NSArray* commandsAsArray()
returns an array with all the commands available, if you need them for helping users.NSString* commandsAsString()
same, but with aNSString*
.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 tocd
to 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 andinputCmd
. (drop-in replacement forpopen
).
replaceCommand: 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.
Sample use: 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 ls
(if false
) or all the commands that used the function previously associated with ls
(if true). For example, compress
and uncompress
are both done with the same function, compress_main
(and the actual behaviour depends on argv[0]
). 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.
addCommandList: 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 dlsym()
), or SELF
if it is defined inside ios_system.framework
(equivalent to RTLD_SELF
).
Example:
<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[0]
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 fork()
, and 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 execv
.
ios_execve
also exists, but is just a pointer to ios_execv
(we don't do anything with the environment for now).
ios_system
is OpenSource; you can extend it in any way you want. Keep in mind the intrinsic limitations:
- Sandbox and API limitations still apply. Commands that require root privilege (like
traceroute
) are impossible. - Inside terminals we have limited interaction. Apps that require user input are unlikely to get it, or with no visual feedback. That could be solved, but it is hard.
To add a command:
- (Optional) create an issue: https://github.com/holzschu/ios_system/issues That will let others know you're working on it, and possibly join forces with you (that's the beauty of OpenSource).
- find the source code for the command, preferrably with BSD license. Apple OpenSource is a good place to start. Compile it first for OSX, to see if it works, and go through configuration.
- make the following changes to the code:
- change the
main()
function intocommand_main()
. - include
ios_error.h
. - link with
ios_system.framework
; this will replace most function calls byios_system
version (exit
,warn
,err
,errx
,warnx
,printf
,write
...) - replace calls to
isatty()
with calls toios_isatty()
. - usually, this is enough for your command to compile, and sometimes to run. Check that it works.
- if you have no output: find where the output happens. Within
ios_system
, standard output must go tothread_stout
.libc_replacement.c
intercepts most of the output functions, but not all. - if you have issues with input: find where it happens. Standard input comes from
thread_stdin
. - make sure you initialize all variables at startup, and release all memory on exit.
- make all global variables thread-local with
__thread
, make sure local variables are marked withstatic
. - make sure your code doesn't use commands that don't work in a sandbox:
fork
,exec
,system
,popen
,isExecutableFileAtPath
,access
... (some of these fail at compile time, others fail silently at run time). - compile the digital library, add it to the embedded frameworks of your app.
- Edit the
Resources/extraCommandsDictionary.plist
to add your command, and run. - That's it.
- Test a lot. Side effects can appear after several launches.
- if your command has a large code base, work out the difference in your edits and make a patch, rather than commit the entire code. See
get_sources_for_patching.sh
for an example.
- change the
Frequently asked commands: here is a list of commands that are often requested, and my experience with them:
ping
,nslookup
,telnet
: now provided in the network_ios package.traceroute
and most network analysis tools: require root privilege, so impossible inside a sandbox.unzip
: usetar -xz
.nano
,ed
: require user interaction, so currently impossible.vim
: likeed
, but even more difficult (needs to access the entire screen, need to add lines to the keyboard for Escape, Tab... iVim is on the App Store, and can be accessed from inside OpenTerm using theshare
command. My fork of iVim can launch shell commands with:!
. It's easier to make an editor start commands than to make a terminal run an editor.sh
,bash
,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.
As much as possible, I used the BSD version of the tools. More precisely:
- awk: OpenSource license.
- curl, scp, sftp: MIT/X derivate license.
- lua: MIT License.
- python: Python license.
- libssh2: Revised BSD License (a.k.a. 3-clause BSD license).
- egrep, fgrep, grep, gzip, gunzip: Simplified BSD License (2-clause BSD license).
- cat, chflag, compress, cp, date, echo, env, link, ln, printenv, pwd, sed, tar, uncompress, uptime, Revised BSD License (a.k.a. 3-clause BSD license).
- chgrp, chksum, chmod, chown, df, du, groups, id, ls, mkdir, mv, readlink, rm, rmdir, stat, sum, touch, tr, uname, wc, whoami: Original BSD License (4-clause BSD license)
- pdftex, luatex and all TeX-based programs: GNU General Public License.
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).