✎ soc:2009:lynusvaz:notes:scripting_doc:features_added

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The features mentioned here are NOT YET part of mainline gPXE, and are still under development. The modified code can be found in my git repository, in the [[http://git.etherboot.org/?p=people/lynusvaz/gpxe.git;a=shortlog;h=refs/heads/offset|offset]] branch.

Scripting features:

  - Identifiers
  - Arithmetic evaluator
  - Quoting
  - Return code
  - Branches
  - Loops

1. See the Identifiers section at: [[http://etherboot.org/wiki/commandline]], for the basic syntax of an identifier. The new code allows identifiers to be 'nested', like:
  set i 0
  echo ${net${i}/ip}
will print the IP address of the net0 interface. Arithmetic operations (see 2) can also be performed within the ${}:
E.g.:
  set i 0
  echo ${net$(${i}+1)/ip}
will print the IP address of the net1 interface (if it exists).
Identifiers are expanded by placing them within ${}.
E.g.:
  echo $(1 + 2)
  set a 15
  echo $(${a} * 3 + 5)
  echo $( ${net0/ip} != "" )
Output:
  3
  50
  1

2. Arithmetic expressions can be evaluated by placing them within $().
The usual C operators (except assignment) are supported with their usual precendence:
Operators, in order of decreasing precedence:
  - !, ~          (logical NOT and bitwise negation)
  - *, /, %       (multiplication, division, and modulo)
  - +, -          (addition, subtraction)
  - <<, >>        (left- and right-shift)
  - <, <=, >, >=  (inequality)
  - !=, ==        (equal, not equal)
  - &             (bitwise AND)
  - |             (bitwise OR)
  - ^             (bitwise EX-OR)
  - &&            (logical AND)
  - ||            (logical OR)
The == and != operators also act on strings.

3. Quoting:
The \ is used as an escape character. The following sequences are recognised:
  * \<space> Treats the space as part of the command-line argument
  * \<tab> Ditto
  * \<newline> Concatenates the next line to the current line. Both the \ and the newline character are removed
  * \<any other character> Removes the special meaning of the character (if any)

Within single-quotes, all characters lose their special meaning. Within double-quotes, the \ and $ retain their special meaning.
E.g.:
  set message 'Hello World'
  echo '${message} = '${message}
  set message Hello\ \ World
  echo ${message}
  set message Hello\ World\ \#1	#'Hello World #1' is treated as a single argument
  echo ${message}
  echo 'Hello 
  World'
  echo Hello \
  World
  echo It\'s good to see you!
Output:
  ${message} = Hello World
  Hello  World
  Hello World #1
  Hello
  World
  It's good to see you!

4. The return code of the previous statement can be checked using the ${rc} variable.
A value of 0 means that the command completed successfully, while any other value means the command was not successful.

5. Branches:
The keywords if, else and fi are used to branch command execution:
  if <condition>
      <statements>
  fi

  if <condition>
      <statements>
  else		#optional
      <statements>
  fi

A try-catch block is a special kind of branch.
  try
      <crucial statements>	#Call this statment sequence A
  catch
      <backup statements>	#Call this statement sequence B
  done
The statements in sequence A are executed one by one. If any of them fails, execution branches immediately to sequence B. If all the statements in sequence A are executed successfully, execution skips sequence B.

E.g.:
  if $( ${filename} == "" && ${server} != "")
  	echo "No filename"
  else
  	chain tftp://${server}//${filename}
  fi

  try
  	kernel tftp://${server}//${kernel}
  	initrd tftp://${server}//${initrd}
  	boot
  catch
  	echo "Oops: ${rc}"
  done

6. While and for loops have been added:
  while <condition>
  do
  	<statements>
  done
The while loop executes the statement block while the condition is true.

  for <variable> in <value list>
  do
  	<statements>
  done
The variable takes on each value in the value list one by one.

E.g.:
  set i 0
  while $( ${net${i}/mac} != "" )
  do
  	dhcp net${i}
  	if $(${rc} == 0)
  		chain tftp://${server}//${filename}
  	fi
  	set i $( ${i} + 1 )
  done

  for i in 0 1 2 3 $(3 + 1) 5
  do
  	dhcp net${i}
  	if $(${rc} == 0)
  		chain tftp://${server}//${filename}
  	fi
  done
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