Table of Contents

• 1. exec
  • 1.1. Syntax
  • 1.2. Stack Effects
  • 1.3. Description
  • 1.4. PostScript Level
  • 1.5. Examples
  • 1.6. Common Use Cases
    • 1.6.1. Dynamic Code Execution
    • 1.6.2. Executing Stored Procedures
    • 1.6.3. String Evaluation
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. Execution Behavior by Type
  • 1.11. See Also

1. exec

Executes an object immediately.

1.1. Syntax

any exec → –

1.2. Stack Effects

Table 1. Before

Level	Object
0	any (object to execute)

Table 2. After

Level	Object
(varies)	Results depend on object executed

1.3. Description

exec pushes the operand on the execution stack, executing it immediately.

The effect depends on the object’s type and literal/executable attribute:

• Literal objects: Pushed back on operand stack

• Executable arrays (procedures): Elements executed sequentially

• Executable names: Looked up and executed

• Operators: Executed

• Files/strings: Interpreted as PostScript code

1.4. PostScript Level

Level 1 and later

1.5. Examples

Executing a string

(3 2 add) cvx exec  % Returns 5

Executing a name

/add cvx exec  % Error: stackunderflow (no operands)
3 2 /add cvx exec  % Returns 5

Executing a procedure

{ 1 2 add } exec  % Returns 3

Literal vs. executable

/add exec       % Pushes /add (literal)
/add cvx exec   % Executes add operator

1.6. Common Use Cases

1.6.1. Dynamic Code Execution

/operation (add) def
operation cvn cvx exec  % Executes add

1.6.2. Executing Stored Procedures

/handlers 5 dict def
handlers /onClick { handleClick } put

/onClick handlers exch get exec

1.6.3. String Evaluation

(10 20 mul) cvx exec  % Evaluates string: 200

1.7. Common Pitfalls

Literal Objects Not Executed - Literal objects are just pushed back.

123 exec       % Returns 123 (literal integer)
/name exec     % Returns /name (literal name)
{ code } cvlit exec  % Returns { code } (literal array)

Must Use cvx for Strings - Strings must be executable to interpret as code.

(1 2 add) exec      % Pushes string (literal)
(1 2 add) cvx exec  % Evaluates: 3

Security Risk - Executing arbitrary strings can be dangerous.

userInput cvx exec  % Dangerous if userInput malicious!

Check Executable Attribute - Use xcheck to verify before execution.

1.8. Error Conditions

Error	Condition
[stackunderflow]	No operand on stack
(various)	Depends on what is executed

1.9. Implementation Notes

• Pushes object onto execution stack

• Interpreter then processes it normally

• No special overhead (same as normal execution)

• Can execute any PostScript object

1.10. Execution Behavior by Type

Object Type	Literal	Executable
Integer/Real	Pushed on stack	Pushed on stack
Boolean/Null	Pushed on stack	Pushed on stack
String	Pushed on stack	Interpreted as code
Name	Pushed on stack	Looked up and executed
Array	Pushed on stack	Elements executed
Operator	Pushed on stack	Executed
Dictionary	Pushed on stack	Pushed on stack

1.11. See Also

• cvx - Convert to executable

• cvlit - Convert to literal

• xcheck - Check if executable

• stopped - Execute with error catching

• if / ifelse - Conditional execution