This is a basic introduction to the edify scripting language used by Android to run updater-scripts. Before I begin, I learned pretty much everything I know about edify scripting from E. Pete Karelis; so huge credit goes out to him for the contents of this guide.

Lesson number one: Pretty much all of the commands in Edify are functions; they return data to the script when the function call is complete. You can, of course, use the function's return value to establish success or failure, like so:

ifelse(mount("yaffs2", "MTD", "system", "/system") == "system", ui_print("Successfully Mounted!"), ui_print("Mount Failed!");

This command will attempt to mount the MTD partition named "system" to "/system". If the mount succeeds, the script will display Successfully Mounted!, otherwise(else) it will display Mount Failed!

Below are examples of functions used in an Edify Updater-script:

Function Name: mount

Function Syntax: mount(fs_type, partition_type, location, mount_point)

Parameter Details:

fs_type = "yaffs2" | "ext4"
partition_type="MTD" | "EMMC"
location = partition | device
mount_point = target folder to mount FS.

Action: Mounts a filesystem to the defined mount point

Returns: The mount point if successful, null if failed

Function Name: is_mounted

Function Syntax: is_mounted(mount_point)

Parameter Details: mount_point = string, mount point to check if is mounted

Action: Checks if a filesystem is mounted.

Returns: The mount point if mounted, otherwise, returns null

Function Name: unmount

Function Syntax: unmount(mount_point)

Parameter Details: mount_point = string, mount point to unmount

Action: Unmounts the filesystem

Returns: The mount point that was dismounted if successful, otherwise it returns null

Function Name: format

Function Syntax: format(fs_type, partition_type, location)

Parameter Details:

fs_type = string,"yaffs2" | "ext4"
partition_type= string, "MTD" | "EMMC"
location = string, partition | device

Action: Formats a filesystem as specified

Function Name: delete

Function Syntax: delete(file1, file2, ..., fileN)

Parameter Details: string, file to delete

Action: Deletes a file. Must specify at least one file; multiple files can be specified as multiple arguments

Function Name: delete_recursive

Function Syntax: delete_recursive(dir1, dir2,...,dirN)

Parameter Details: string, directory to recursively delete

Action: Deletes a folder and all of its contents. At least 1 directory must be specified; multiple directories can be specified as additional arguments.

Function Name: show_progress

Function Syntax: show_progress(frac, sec)

Parameter Details:

frac = fraction of progress completed
sec = total seconds

Action: Displays flashing progress in the recovery system

Function Name: set_progress

Function Syntax: set_prograss(frac)

Parameter Details: frac=fraction of progress

Function Name: package_extract_dir

Function Syntax: package_extract_dir(package_path, destination_path)

Parameter Details:

package_path = string, directory in package to extract
destination_path = string, target point to extract files to

Action: Extract the all of the files in a directory in the package to the target specified.

Function Name: package_extract_file

Function Syntax:

package_extract_file(package_path)
or
package_extract_file(package_path, destination_path)

Parameter Details:

package_path = string, file in the package you want to extract
destination_path, target folder to extract the file to.

Action: Extracts a single file from your update package to the target specified

Function Name: file_getprop

Function Syntax: file_getprop(file, key)

Parameter Details:

file = string, filename to check
key = string, key in file to return the value of

Action: Checks for a value in a file?

Function Name: symlink

Function Syntax: symlink(target, src1, src2, ..., srcN)

Parameter Details:

target = string, the target of the symbolic link
srcX = the symbolic link to create that points to the target

Action: Unlinks any existing symbolic links before creating the new symbolic links.

Function Name: set_perm

Function Syntax: set_perm(uid, gid, mode, file1, file2, ..., fileN)

Parameter Details:

uid = user id
gid = group id
mode = permission mode
fileX = file to set permission on

Action: Sets permissions of a file or set of files specified. At least one file must be specified (the first four parameters are required)

Function Name: set_perm_recursive

Function Syntax: set_perm_recursive(uid, gid, dirmode, filemode, dir1, dir2, ...dirN)

Parameter Details:

uid = user id
gid = group id
dirmode = permission to set to directories contained within the specified directory
filemode = permission to set to files contained within the specified directory
dirX = directory to set permission on

Action: Set permissions of a directory or set of directories and all files and folders within them. At least one directory must be specified (The first 5 parameters are required)

Function Name: getprop

Function Syntax: getprop(key)

Parameter Details: key = string, the property you want the system to return

Action: This function returns the value of the property specified. This is used to query platform information from the build.props file.

Function Name: write_raw_image

Function Syntax: write_raw_image(file, partition)

Parameter Details:

file - string, the source .img file to be read from
partition - string, the destination partition to write the .img file to

Description: This function writes an img file to a partition.

Function Name: apply_patch

Function Syntax: apply_patch(srcfile, tgtfile, tgtsha1, tgtsize, sha1_1, patch_1, ..., sha1_x, patch1_x)

Parameter Details:

srcfile - string, source file to be patched (file to read in)
tgtfile - string, destination file to write the patched file to
tgtsha1 - string, sha1 hash of the target file as it should hash out after the patches apply properly
sha1_x - string, sha1 hash of the patch data that's to be written to the target file
patch1_x- string, actual patch to apply to the target file

Action: This function is used to apply patches to a file.

Function Name: apply_patch_check

Function Syntax: apply_patch_check(file, sha1_1, ..., sha1_x)

Parameter Details:

file - string, file to check
sha1_x - hash to check for?

Action: Either checks if a file has been properly patched, or checks if a file can be patched. Need to check the source code of the "applypatch_check" function that is called from here.

Function Name: apply_patch_space

Function Syntax: apply_patch_space(bytes)

Parameter Details: bytes = number of bytes to check for

Action: Checks the cache to verify that there is enough space to write the patched files to it and returns something. Need to test this function to verify.

Function Name: read_file

Function Syntax: read_file(filename)

Parameter Details: filename - string, the filename to read the contents of

Action: This function returns the contents of a file.

Function Name: sha1_check

Function Syntax:

sha1_check(data)
or
sha1_check(data, sha1_hex, ..., sha1_hexN)

Parameter Details:

data - the contents of file to calculate the sha1 hash of - must be in the read_file format
sha1_hexN - A particular sha1_hex string that you want the file data to match

Action: If only data is specified, then the function returns the sha1_hex string of the data. The optional parameters are used if you want to verify that the file you are checking for is one of a list of hashes. It reutrns the hash it matches, or returns nothing if it doesn't match any of the mentioned hashses.

Function Name: ui_print

Function Syntax: ui_print(msg1, ..., msgN)

Parameter Details: msg - String, message to be outputted to the user during the patch process

Action: This function prints/echos a message to the console while the script is running. At least 1 parameter needs to be specified, you can specify additional msg parameters and they will be concatenated to the output.

Function Name: run_program

Function Syntax: run_program(prog, arg1, .., argN)

Parameter Details:

prog - string, program to execute
argN - string, arguments for the program that is being executed
Description: Executes a program with the arguments specified. Returns a string, I assume it is the buffer of the stdout of the program executed, need to test.

Function Name: ifelse

Function Syntax: ifelse(condition, truecondition, falsecondition)

Parameter Details:

condition - an expression to evaluate
truecondition - Edify script block to execute if true
falsecodnition - Edify script block to execute if false

Description: This is the if-then construct of the Edify scripting language. The truecondition or falsecondition arguments can be a single edify command or a script block. Script blocks can be formed by enclosing the parameter with parenthesis, and seperating the commands with semicolons\

Function Name: abort

Function Syntax: abort()

Parameter Details: no paremeters

Description: Aborts script execution.

Function Name: assert

Function Syntax: assert(condition)

Parameter Details: condition - boolean

Description: If condition evaluates to false, stops script execution, otherwise continues processing.

There are more functions than have been mentioned above, and I will continue to update this list as and when possible!