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--- soc:2009:lynusvaz:notes:scripting_doc:features_added [2009/08/05 09:30]
lynusvaz created
+++ soc:2009:lynusvaz:notes:scripting_doc:features_added [2009/08/16 00:19] (current)
lynusvaz
@@ Line 1: / Line 1: @@
-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=====
+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/expt|expt]] branch.
-Scripting features:
+  - Identifiers
+  - Arithmetic evaluator
+  - Quoting
+  - Branches
+  - Return code
+  - Loops
-. Identifiers
+====Identifiers====
-. Arithmetic evaluator
+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:
-. Quoting
+  set i 0
-. Return code of commands
+  echo ${net${i}/ip}
-. Branches
+will print the IP address of the net0 interface. Arithmetic operations (see 2) can also be performed within the ${}:
-. Loops
+E.g.:
+  set i 0
-. 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:
+  echo ${net$(${i}+1)/ip}
-set i 0
+will print the IP address of the net1 interface (if it exists).
-echo ${net${i}/ip}
-will print the IP address of the net0 interface.
-. Arithmetic expressions can be evaluated by placing them within $().
+====Arithmetic Evaluation====
-The usual C operators (except assignment) are supported with their usual precendence. Also, string comparison is permitted.
+Arithmetic expressions can be evaluated by placing them within $().
-Identifiers are expanded by placing them within ${}.
+The following operators are supported (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. Identifiers are expanded by placing them within ${}.
 E.g.:
-echo $(1 + 2)
+  echo $(1 + 2)
-set a 15
+  set a 15
-echo $(${a} * 3 + 5)
+  echo $(${a} * 3 + 5)
-echo $( ${net0/ip} != "" )
+  echo $( ${net0/ip} != "" )
+Output:
+
+
-. Quoting:
+====Quoting====
 The \ is used as an escape character. The following sequences are recognised:
-\<space> Treats the space as part of the command-line argument
+  * \<space> Treats the space as part of the command-line argument
-\<tab> Ditto
+  * \<tab> Ditto
-\<newline> Concatenates the next line to the current line. Both the \ and the newline character are removed
+  * \<newline> Concatenates the next line to the current line. Both the \ and the newline character are removed
-\\ A literal \
+  * \<any other character> Removes the special meaning of the character (if any)
-\<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. Single- and double-quotes allow you to use a newline character in a command-line argument.
-Within single-quotes, all characters lose their special meaning. Within double-quotes, the \ and $ retain their special meaning.
 E.g.:
-set message 'Hello World'
+  set message "Hello World"
-echo '${message} = '${message}
+  echo '${message} = '${message}
-set message Hello\ \ World
+  set message Hello\ \ World
-set message Hello\ World\ \#1	#'Hello World #1' is treated as a single argument
+  echo ${message}
-echo 'Hello
+  set message Hello\ World\ \#1	#'Hello World #1' is treated as a single argument
-World'
+  echo ${message}
-echo Hello \
+  echo 'Hello
-World
+  World'  # Will introduce a newline between Hello and World
-echo It\'s good to see you!
+  echo Hello \
+  World
+  echo It\'s good to see you!
+Output:
+  ${message} = Hello World
+  Hello  World
+  Hello World #1
+  Hello
+  World
+  Hello World
+  It's good to see you!
-. The return code of the previous statement can be checked using the ${rc} variable.
+====Branches====
-A value of 0 means that the command completed successfully, while any other value means the command was not successful.
-. Branches:
 The keywords if, else and fi are used to branch command execution:
-if <condition>
+  if <condition>
-	<statements>
+      <statements>
-fi
+  fi
-if <condition>
+  if <condition>
-	<statements>
+      <statements>
-else		#optional
+  else		#optional
-	<statements>
+      <statements>
-fi
+  fi
 A try-catch block is a special kind of branch.
-try
+  try
-	<crucial statements>	#Call this statment sequence A
+      <crucial statements>	#Call this statment sequence A
-catch
+  catch
-	<backup statements>	#Call this statement sequence B
+      <backup statements>	#Call this statement sequence B
-done
+  done
-The statements in sequence A are executed one by one. If any of them fails, execution branches immediately to sequence B.
+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, and continue after the done statement.
 E.g.:
-if $( ${filename} == "")
+  if $( ${filename} != "" && ${server} != "")
-	echo "No filename"
+  	chain tftp://${server}//${filename}
-else
+  else
-	chain tftp://${server}//${filename}
+  	echo "No filename"
-fi
+  fi
+will first check that neither filename and server are not empty, before attempting to boot. If either is empty, display an error message.
-try
+  try
-	kernel tftp://${server}//${kernel}
+  	kernel tftp://${server}//${kernel}
-	initrd tftp://${server}//${initrd}
+  	initrd tftp://${server}//${initrd}
-	boot
+  	boot
-catch
+  catch
-	echo "Oops: ${rc}"
+  	echo "Oops: ${rc}"
-done
+  done
+will attempt to boot using the given kernel and initrd. If any of the three commands fail, it displays a message.
-. While and for loops have been added:
+====Return Code====
-while <condition>
+The return code of the previous statement can be checked using the ${rc} variable.
-do
+A value of 0 means that the command completed successfully, while any other value means the command was not successful.
-	<statements>
-done
+E.g.:
+  dhcp net0
+  if $( ${rc} != 0 )
+      echo "DHCP failed"
+  else
+      chain http://etherboot.org/gtest/gtest.gpxe # (Tom's Root Boot disk)
+  fi
+====Loops====
+You can use while and for loops as:
+  while <condition>
+  do
+  	<statements>
+  done
 The while loop executes the statement block while the condition is true.
-for <variable> in <value list>
+  for <variable> in <value list>
-do
+  do
-	<statements>
+  	<statements>
-done
+  done
 The variable takes on each value in the value list one by one.
 E.g.:
-set i 0
+  set i 0
-while $( ${net${i}/mac} != "" )
+  while $( ${net${i}/mac} != "" )
-do
+  do
-	dhcp net${i}
+  	dhcp net${i}
-	if $(${rc} == 0)
+  	if $(${rc} == 0)
-		chain tftp://${server}//${filename}
+  		chain tftp://${server}//${filename}
-	fi
+  	fi
-	set i $( ${i} + 1 )
+  	set i $( ${i} + 1 )
-done
+  done
+will attempt to get a dhcp connection on each valid interface, and if it is successful, boot using a given file.
-for i in 0 1 2 3 $(3 + 1) 5
-do
-	dhcp net${i}
-	if $(${rc} == 0)
-		chain tftp://${server}//${filename}
-	fi
-done
+  for i in 0 1 2 3 5 $(6*3)
+  do
+        echo 'i =' ${i}
+  done
+displays:
+  i = 0
+  i = 1
+  i = 2
+  i = 3
+  i = 5
+  i = 18
+A break statement will exit a loop, and a continue statement will start the next iteration of the loop.
+  for i in 1 2 3 4 5 6
+  do
+        if $(${i} == 3)
+              continue
+        fi
+        echo 'i =' ${i}
+        if $(${i} == 4)
+              break      #This will exit the for loop, not just the if branch
+        fi
+  done
+displays:
+  i = 1
+  i = 2
+  i = 4

Trace: • features_added

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