EFI Shells and Scripting

Introduction

Extensible firmware interface (EFI) brings new flexibility and opportunities to users by allowing them to work in the layer between their OS and BIOS, without altering either one. This paper explains how to use EFI shell commands, create a script file and set up the boot menu with shells and scripts. In addition, this paper demonstrates dual boot selection for the 64-bit Red Hat Linux* 7.1 and 64-bit Microsoft Windows* XP Professional operating systems.


EFI Shell Commands

The following is the list of the EFI 0.99[12.29] shell commands:

Commands Descriptions
help [-b] [internal command] Displays this help
guid [-b] [sname] Lists known GUID (Global Unique Identifiers)
set [-bdv] [sname] [value] Gets or sets environment variable
alias [-bdv] [sname] [value] Gets or sets alias settings
dh [-b] [-p prot_id] | [handle] Dumps handle information
unload [-nv] HandleIndex Unloads a protocol image
map [-bdvr] [sname[:]] [handle] Maps shortname to device path
mount BlkDevice [sname[:]] Mounts a file system on a block device
cd [path] Updates the current directory
echo [[-on | -off] | [text] Echoes text to stdout or toggle script echo
if [not] condition then Script-only: IF THEN construct
endif Script-only: Delimiter for IF THEN construct
goto label Script-only: Jump to label location in script
for var in <set>< /td> Script-only: Loop construct
endfor Script-only: Delimiter for loop construct
pause Script-only: Prompt to quit or continue
ls [-b] [dir] [dir] ... Obtains directory listing
mkdir dir [dir] ... Makes directory
mode [col row] Gets or sets current text mode
cp [-r] file [file] ... [dest] Copies files/directories
comp file1 file2 Compares two files
rm file/dir [file/dir] Remove files/directories
memmap [-b] Dumps memory map
type [-a] [-u] [-b] file Types file
dmpstore Dumps variable store
load driver_name Loads a driver
ver Displays version information
err [level] Sets or displays error level
time [hh:mm:ss] Gets or sets time
date [mm/dd/yyyy] Gets or sets date
stall microseconds Delay for x microseconds
reset [/warm] [reset string] Cold or warm reset
vol fs [Volume Label] Sets or displays volume label
attrib [-b] [+/- rhs] [file] Sets or displays file attributes
cls [background color] Clears screen
bcfg -? Configures boot driver and load options
edit [file name] Edits a file
Edd30 [On | Off] Enables or disables EDD 3.0 device paths
dblk device [Lba] [Blocks] Hex dump of BlkIo devices
pci [bus dev] [func] Displays PCI device(s) information
mm Address [Width] [;Type] Modifies memory: Mem, MMIO, IO, PCI
mem [Address] [size] [;MMIO] Dumps memory or memory mapped IO
EddDebug [BlockDeviceName] Dumps EDD information from adapter card

Table 1: EFI 0.99[12.29] shell commands

This list appears when you type the command "help" at the shell prompt. However, it does not contain all of the EFI shell commands; the commands "attrib" and "exit" are absent. Not all commands can be used in script files. For example, the command "exit" missing from the list cannot be used in a script file. To exit out of a script, simply jump to the end of the file. Conversely, some of the commands like "if...then," "for...in," "goto" can only be used inside the script file.

To execute a command, type it at the shell prompt, which can be as follows:

Shell>

fs0:> (If there is a disk in the floppydrive before the PC is turned on, then the current media defaults to the floppy disk. If not, then the current media is the first hard disk partition.)
fs1:> (The first hard disk partition if fs0 is the floppy disk.)
fs2:> (Indicates the CD-ROM drive.)

This environment is similar to Microsoft DOS* (MS-DOS) in that the user types in commands and presses "Enter" to execute the commands. As demonstrated below, changing to another drive is easy: type the name of the drive and then press "Enter". ("<CR>" is a "carriage return" which translates to "press Enter.")

Shell> fs0: <CR>
Fs0:> fs2: <CR>

Fs2:>

If the user is unfamiliar with the use of a command, they simply type it at the shell prompt and the computer displays the correct syntax and meaning of each of the switches.


EFI Shell Scripts

In basic terms, a script file is one that contains a sequence of shell commands that the user would like the computer to execute. Rather than entering them at the shell prompt, the user places the appropriate shell commands into a file and names the file "filename.nsh" to create a script file. This is extremely useful for repetitive tasks.

The script file resembles a batch file in MS-DOS; in EFI, a file called "startup.nsh" automatically runs every time a shell environment is opened. You can create the script using any ASCII or Unicode text editor. The following are shell commands frequently used in a script:

3.1 Echo:

    Syntax:echo [-on |

    -off]

    echo [text]

The first line in a script is usually "echo -off." This prevents subsequent batch file commands from displaying on the screen so that only results display.

For example, in a script file, there are such commands:

    
Batch commands:echo -on
echo This is a test

When you run that script, you see the following lines on the screen:

    Result:echo -on

    echo This is a test

    This is a test
    

The first two lines in bold are batch commands from the script, and the third line is the result of the second batch command. Note the display when the echo command is turned off:

    Batch commands:echo -off

    echo This is a test

    Result:echo -off

    This is a test

The batch command "echo This is a test" no longer displays onscreen because the echo has been turned off. You always see the batch command "echo -off" because the echo does not disable after this line has been executed.

3.2 If

    Syntax:if [not] exist filename then

    ...

    endif

    if [not] string1 == string2

    then
...
endif

The first form checks for file existence. Type either just the file name or the path and the file name. For example:

    set test "startup.nsh" # Assign "startup.nsh" to the

    environment

     # variable named test

    if exist %test% then # Check to see if the file

    "startup.nsh"

     # exists in the current directory

    type %test% # Displays the contents of "startup.nsh"

     # if found.

    endif # End of if ... then statement

The second form is the comparison between strings:

    set env1 "world"

    set env2 "map"

    if %env1% == %env2% then # Compare the value of 2

    variables

    echo %env1% is equal to %env2%

    endif

Note: Spaces need to be inserted at both ends of the "==" sign. Otherwise, the shell generates an error.

    %env1% == %env2% correct

    %env1%==%env2% incorrect

3.3 For

    Syntax:for %index in

    group

    ...

    endfor

This is a "for" loop. The index here is any single character, like a, b, c and so on, but it can't be a digit like 1, 2 or 3 because they can be misinterpreted as "argument" variables. Groups can be made up of strings or file names separated by the use of spaces. Consider the following examples:

    Batch commands:for %b in 1

    2 3 4

    type %b

    **

    endfor

    Result:1

    **

    2

    **

    3

    **

    4

    **

    Batch commands:for %m in

    *.nsh

    type

    %m

     endfor

Result: The list of all files with extension "nsh" in the current directory.

Note: Spaces need to be inserted at both ends of the %index. Otherwise, the shell generates an error.

    Type %b ** correct

    Type %b** incorrect

Dual Boot Selection

Consider the procedure for setting up dual boot on an Intel Itanium processor-based system. If Windows* 9x and Windows NT* or Windows* 2000 is installed on an Intel® Itanium® platform, you can set up a dual boot under Windows NT or Windows 2000. If Windows 9x and Linux are installed, you can set up a dual boot under Linux.

On the Intel Itanium platform, there is a layer between the firmware and the OS—that layer is the EFI. You can boot to any installed OS from the EFI layer as long as the OS is EFI-compliant.

Below is a demonstration of dual booting 64-bit versions of Red Hat Linux* and Microsoft Windows* 2000.

Before starting to build the boot menu:

A) You must disable the file "startup.nsh." This script runs automatically when you turn on the system and select the "Boot OS" option. When you install Windows 2000, it creates the "startup.nsh" file. This file executes a file called "launcher.efi," which boots directly to Windows 2000. Perform the following steps to disable the startup.nsh file:

1) During the Windows booting process, press any key to interrupt it.

2) Change the access right of the startup.nsh file to modify or delete it. From the shell prompt, "Shell>," go to the main partition:

Shell> fs0:

     or 

Shell> fs1:

The choice between "fs0" and "fs1" depends on whether a disk is in the floppy drive.

Note: To use the floppy drive, a floppy disk must be inserted. Otherwise, the floppy drive is not recognized; the same caution applies to the CD-ROM drive.

fs0:> attrib -r startup.nshfs0:> edit startup.nsh

In edit mode, type a # sign at the beginning of the line containing the word "launcher" to comment it out.

B) Make sure the BIOS build 89B is flashed. One way to establish the correct build number is to look at the EFI version when you first turn on the PC; if it's correct, you see something like:

EFI Version 0.99[12.31]...

There are instances in which an incorrect BIOS version has been preloaded to the Software Development Vehicle (SDV). If you see "EFI Version 1.0[12.25]..." displayed on the screen, reflash the BIOS with build 89B or 99.

Assume you want the following multiple boot menu:

  • Windows XP* Professional
  • Red Hat Linux*
  • EFI Shell

You can create it using any of these methods:

  • boot maintenance menu
  • BCFG command
  • script

4.1 Using Boot Maintenance Menu:

Follow these steps to create a boot menu:

1) Turn on the system.

2) Select "Boot OS."

3) At the shell prompt, type "exit" and press Enter.

Shell> exit

4) The screen displays a boot menu similar to the following:

EFI Boot Manager ver. 0.99[12.29]

Select boot option

EFI Shell [built in]

Boot option maintenance menu

5) Select the boot option maintenance menu.

6) Select "Add a boot option."

7) Select the partition containing the OS loader. In this case, it is the first hard disk partition. Something similar to the following appears onscreen:

NO VOLUME LABEL [VenHw(Unknown D evice:80)/HD(Part1, Sig948939)]

Removable Media [VenHw(Unknown Device:01)]

Removable Media [VenHw(Unknown Device:FF)]

Load File [Acpi(PNP0A03,0)/Pci(4|0)/mac(009027E4A0F4)]

Load File [EFI Shell [Built-in]]

Legacy Boot A:

Legacy Boot C:

Exit

8) Select the first item, "NO VOLUME LABEL..."

9) The screen displays the files of the directory of the selected partition.

Select the file "eli.efi." This is the Linux loader file.

10) Type the title you wish to display on the boot menu when asked for the description: "Red Hat Linux*."

11) When prompted with:

"New boot option data: ASCII/Unicode string only Enter Boot option Data type[A- SCII U- Unicode N- No BootOption]," select "N."

12) Next, select the option "Save Changes to NVRAM[Y-yes N-No]:" and type "Y."

13) When you have no other OS to set, select "exit" to return to the previous menu.

14) Select "Cold Reset" to reboot the system.

15) To create an EFI shell prompt, select option "EFI Shell[built in]" from step 7 and type "EFI Shell" at step 10.

16) Type "exit" at the shell prompt "Shell>" to go to the boot menu.

4.2 Using the BCFG Command

The "Bcfg" is the boot configuration shell command. Assuming that "fs0" is the main partition, type the following statement to create the boot menu:

fs0:> bcfg boot add 2 eli.efi "Red Hat Linux*"

Note: You cannot create an EFI shell prompt using this method; you must use the previous method.

4.3 Using Script

Since there is no user-prompt command under the EFI shell to accept users' selected input, you must use an alternative method:

a) If the file startup.nsh does not exist,

create it or modify it to

contain strictly the following line:

    Menu

b) Create a file and name it menu.nsh with the following:

 

    Echo -off

Dblk3:

Echo 2- Red Hat Linux

Echo Enter choice and press Enter

Note:

1) There is no option for the shell prompt since the command "nshell" is not on the list.

2) The current partition is set to "dblk3" instead of "fs0" or "fs1." This is because if there is a floppy disk in the floppy drive, then "fs0" is the floppy disk and "fs1" is the first hard disk partition. Otherwise, "fs0" is the first hard disk partition

.

c) Create a file and name it "2.nsh" with the following contents:

eli

Note: The "2.nsh" script is used to boot to Red Hat Linux*.

Conclusion

This represents only the beginning of the uses and benefits of EFI shell commands and scripts. Not only can EFI be used similarly to a MS-DOS device driver, its capabilities also remove the hassle of modifying the OS. Disk utility vendors can use EFI to craft powerful tools like platform-independent disk partitioning. Another of EFI's benefits is that the same device drivers can be used by many EFI-compliant platforms, thus providing a good return on investment. EFI allows users to create device drivers to access hardware directly without having to go through the OS, making the process both simpler and faster.


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