Table of Contents

• 1. anchorsearch
  • 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. Protocol Detection
    • 1.6.2. Comment Stripping
    • 1.6.3. File Extension Detection
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. See Also

1. anchorsearch

Tests whether a string begins with a specified prefix.

1.1. Syntax

string seek anchorsearch → post match true (if found)
                          → string false (if not found)

1.2. Stack Effects

Table 1. Before

Level	Object
1	string (string to search in)
0	seek (prefix to search for)

Table 2. After (if match found)

Level	Object
2	true
1	match (matching prefix portion)
0	post (remainder after prefix)

Table 3. After (if not found)

Level	Object
1	false
0	string (original, unchanged)

1.3. Description

anchorsearch determines if string begins with seek (i.e., string is at least as long as seek and the initial characters match exactly).

If it matches: * Splits string into match (the matching prefix) and post (the remainder) * Pushes post, match, and true

If not: * Pushes the original string and false

The match is case-sensitive and must occur at the start of string.

1.4. PostScript Level

Level 1 and later

1.5. Examples

Successful prefix match

(abbc) (ab) anchorsearch
% Result: (bc) (ab) true

No match - wrong position

(abbc) (bb) anchorsearch
% Result: (abbc) false
% 'bb' exists but not at start

No match - not present

(abbc) (xyz) anchorsearch
% Result: (abbc) false

Case sensitivity

(Hello) (he) anchorsearch
% Result: (Hello) false  ('he' != 'He')

1.6. Common Use Cases

1.6.1. Protocol Detection

url (http://) anchorsearch {
  pop  % post (rest of URL)
  % Handle HTTP URL
} {
  pop  % original string
  % Try other protocols
} ifelse

1.6.2. Comment Stripping

line (%) anchorsearch {
  pop pop  % Discard comment
} {
  % Process line
} ifelse

1.6.3. File Extension Detection

filename (.ps) anchorsearch {
  % PostScript file
} {
  % Other file type
} ifelse

1.7. Common Pitfalls

Must Match At Start - anchorsearch only finds prefixes, not substrings anywhere in the string.

(hello) (ll) anchorsearch  % false - not at start

Case Sensitive - Matching is exact, including case.

(PostScript) (post) anchorsearch  % false

Use search for Anywhere - For substring search anywhere in string, use search instead.

1.8. Error Conditions

Error	Condition
[invalidaccess]	String has no-access attribute
[stackoverflow]	Not enough room on stack for results
[stackunderflow]	Fewer than 2 operands on stack
[typecheck]	Either operand is not a string

1.9. Implementation Notes

• Very efficient - stops checking after first mismatch

• Returns substring objects that share the original string value

• Empty seek string always matches (returns entire string as post, empty match)

1.10. See Also

• search - Search for substring anywhere

• token - Parse token from string

• getinterval - Extract substring