A "shell" is a program that listens to keyboard input from a user and performs actions as directed by the user. Android devices come with a simple shell program. This shell program is mostly undocumented. Since many people are curious about it I thought I'd write up some documentation for it.
Currently this documentation is incomplete, sorry!
The built-in shell has very limited error handling. When you type a command name incorrectly it will say "permission denied", even though the real problem is that it couldn't find the command:
$ dir dir: permission denied <---- this is a misleading error message, should say 'dir: not found' $ ls ... listing of current directory
The Android shell will run any program it finds in its PATH. The PATH is a colon (':') seperated list of directories. You can find out what your shell's PATH is set to by using the built-in echo command:
$ echo $PATH /data/local/bin:/sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin
Depending upon your shell, you may see a different result.
Every shell has a few built-in commands. Some common built-in commands are:
To find out what commands you have available to you, use the "ls" command on each of the directories in the PATH variable.
Many of the Android commands are based on standard Linux (or bsd) commands. If you're curious about a command, you can sometimes learn how it works by using the "man" command on a desktop Linux or OSX (Apple Macintosh) computer. The Linux or OSX version of the command may be different in details, but much of the documentation will still apply to the Android version of the command.
Another source of documentation for people without a Linux or OSX machine handy is to use a web browser and use a web search engine to search for the text: "man Linux command-name".
The following is a list of the commands that are present on a Nexus S phone running an Android 2.3.3 "user-debug" build. Many of these commands are not present on a "user" phone. (They are missing from a "user" phone because they are specific to developing or debugging the Android operating system.)
$ ls /data/local/bin /data/local/bin: No such file or directory
Notice that by default there is no /data/local/bin directory. You can create this directory using the "mkdir" command if you like.
$ ls /sbin opendir failed, Permission denied
The /sbin directory exists, but you don't have permission to access it. You need root access. If you have a developer phone, or otherwise have root access to your phone you can see what's in this directory.
$ su # ls /sbin ueventd adbd # exit $
Notice that the shell prompt changes from a '$' to a '#' to indicate that you have root access.
Notice also that neither of the /sbin commands are useful to the shell -- the adb and ueventd files are 'daemon' programs used to implement the Android Debugger "adb" program that is used by developers.
$ ls /vendor/bin gpsd pvrsrvinit
Vendor/bin is where device vendors can put device-specific executables. These files are from a Nexus S.
$ ls /system/sbin /system/sbin: No such file or directory
This directory does not exist on a Nexus S.
$ ls /system/bin am
am is the Android Activity Manager. It's used to start and stop Android activities (e.g. applications) from the command line. Type am by itself to get a list of options.
Command line audio file player.
Used to apply patches to android files.
Command line audio recorder.
Backup manager - type command by itself to get documentation.
Draws the boot animation. You may have to reset your phone to get out of this.
brcm_patchram_plus bugreport cat
Copy the contents of a file to standard output.
Change the mode of a file (e.g. whether it can be read or written.)
Change the owner of a file.
Compare two files byte-by-byte
The dalvik virtual machine. (Used to run Android applications.)
Prints the current date and time
Convert and copy a file. By default copies standard in to standard out.
debuggerd dexopt df
Shows how much space is free on different file systems on your device.
dhcpcd dmesg dnsmasq dumpstate dumpsys dvz fsck_msdos gdbserver getevent getprop gzip hciattach hd id ifconfig
Shows the current configuration of network interfaces (IP, MAC address etc)
Shows the current processes using the network interfaces (top, but for networks)
ime input insmod installd ioctl ionice iptables
Manage the firewall
keystore keystore_cli kill
Send signals to processes.
Used to set up a file system link.
Prints the Android runtime log.
lsmod lsof make_ext4fs mediaserver mkdir
Make a directory.
A program that sends random events, used to test applications. (Like having a monkey playing with the device.)
mount mtpd mv
Move a file from one directory to another. (Only on the same file system. Use "cat a > b" to copy a file between file systems.
nandread ndc netcfg netd netstat newfs_msdos notify omx_tests pand ping pm pppd printenv ps
List active processes.
qemu-props qemud racoon radiooptions reboot
Reboot the device.
record renice rild rm
Remove a file.
Remove a directory.
rmmod route rtp_test run-as schedtest schedtop sdcard sdptool sendevent service servicemanager setconsole setprop setup_fs sh showlease sleep smd stagefright start
Starts the Android runtime.
Stops the Android runtime.
surfaceflinger svc sync system_server tc testid3 toolbox top
Shows which processes are currently using the most CPU time.
Prints how long your device has been running since it was last booted.
vdc vmstat vold watchprops wipe wpa_cli wpa_supplicant $ ls /system/xbin add-property-tag btool check-lost+found dexdump dhdutil hcidump latencytop librank opcontrol oprofiled procmem procrank rawbu scp
Secure copy program. (Used to copy files over the network.)
showmap showslab sqlite3
Used to administer SQLite databases.
System trace command - use to see what system calls a program makes.
Start a shell with root privileges.
Busybox is a program that contains a shell and a set of command line utilities. Search Android Market for "Busybox" and you should find some versions you can install. The Busybox shell includes tab completion and history editing. Some versions of Busybox for Android do not require that you root your phone.
You can install the full Debian shell and utilities. (Debian is a popular desktop Linux distribution.) I don't know the details, and it may require a "rooted" phone. Try a web search for "Debian Android install".
Some custom ROMs come with their own shells and utilities. If you are using a custom ROM, check its documentation to find out what's available.