Using Patterns in Parsing

Patterns can be included in the template. Their purpose is to break down the string into substrings prior to the actual parsing into words process. Parsing will then be performed, as previously described, on the substrings and not on the original string.

Two types of patterns are available:

• String Patterns – a character string delimited by quotes, to distinguish it from a variable name
• Numeric (Positional) Patterns – a number, signed or unsigned

Using String Patterns

The string is scanned from left to right for a substring that matches the string pattern.

The following situations may occur:

• A match is found, that is, a substring within the string is identical to the given string pattern.

  The original string is divided into two substrings. The first substring (up to, but not including, the string pattern) is parsed into words using the variables named before the string pattern on the template. Parsing continues from the character following the matched string.

  Example

  DO SET=%%S= THIS IS A SAMPLE STRING

  DO SET=%%T= A1 A2 'SAMPLE' A3 A4 A5

  DO SET=%%$PARSE %%S %%T

  A match is found since the string SAMPLE is part of the original string.

  The %%$PARSRC System variable, which is discussed in %%$PARSE, can be used to check if all strings specified in the template were matched during the parsing process.

  The original string is divided into two substrings while the matched part of the string is excluded. Parsing of the first substring will use the variables listed before the match on the template while parsing of the second substring will use the variables listed after the match:

  • First substring: THIS IS A

    As a result of parsing

    A1=THIS
A2=IS A

  • Second substring: STRING

    As a result of parsing:

    A3=STRING
A4=NULL
A5=NULL

  A match is not found. There is no substring identical to the given string pattern within the string.

  It is assumed that a match is found at the end of the string. The first substring consists of the entire string and it is parsed using only the variables named before the string pattern on the template. Parsing continues from the character following the matched string (the end of the string, in this case).

  Example

  DO SET=%%S = THIS IS A SAMPLE STRING
DO SET=%%T = A1 A2 A3 'EASY' A4 A5
DO SET=%%$PARSE %%S %%T

  A match was not found. The string ‘EASY’ does not exist within the original string.

  • First substring: THIS IS A SAMPLE STRING

    As a result of parsing:

    A1=THIS
A2=IS
A3=A SAMPLE STRING

  • Second substring: NULL

    As a result of parsing:

    A4=NULL
A5=NULL

Using Numeric Patterns Within the Template

Numeric patterns are numbers that mark positions in the string. They are used to break the original string into substrings at the position indicated by the number.

The position specified can be absolute or relative:

• An absolute position is specified by an unsigned number.
• A relative position is specified by a signed number (positive or negative) and its purpose it to determine a new position within the string, relative to the last position.
• The last position is one of the following:
  • the start of the string (position 1), if the last position was not specified previously
  • the starting position of a string pattern if a match was found
  • the position of the end of the string, if the string pattern was not matched
  • the last position specified by a numeric pattern
• If the specified position exceeds the length of the string, the numeric pattern is adjusted to the end of the string. Similarly, if the specified position precedes the beginning of the string (negative or zero numeric pattern), then the beginning of the string is used as last position.

  Example 1

  A parsing template with an absolute numeric pattern:

  DO SET=%%S =THIS IS A SAMPLE STRING

  DO SET=%%T = A1 A2 11 A3 A4 A5

  DO SET=%%$PARSE %%S %%T

• First substring: THIS IS A (up to, but not including, position 11)

  As a result of parsing

  A1=THIS
A2=IS A

• Second substring: SAMPLE STRING (from position 11, up to the end of the string).

  As a result of parsing

  A3=SAMPLE
A4=STRING
A5=NULL (0 length string)

  Example 2

  A parsing template with a relative numeric pattern:

  DO SET=%%S =THIS IS A SAMPLE STRING

  DO SET=%%T = A1 A2 +10 A3 A4 A5

  DO SET=%%$PARSE %%S %%T

Last position is the beginning of the string (position 1).

Position marked within the string is 1 + 10 = 11.

• First substring: THIS IS A (up to, but not including, position 11)

  As a result of parsing

  A1=THIS
A2=IS A

• Second substring: SAMPLE STRING (from position 11, up to the end of the string).

  As a result of parsing:

  A3=SAMPLE
A4=STRING
A5=NULL (0 length string)

Using More Than One Pattern and Combining Pattern Types in the Template

Both types of patterns (string and numeric) can be combined in the same template. Up to 30 patterns and up to 30 variable names can be specified.

Scanning of the string proceeds from beginning of the string until the first pattern (if any).

1. String pattern – A match was found

   The substring that precedes the match to the pattern is parsed using the variables named in the template before the pattern, with the last variable receiving the end of the substring, including leading and trailing blanks.

2. String pattern – A match was not found

   Since no match was found in the string, it is assumed that a match is found at the end of the string. The whole string is parsed using only the variables named in the template before the pattern.

3. Numeric pattern (absolute)

   The absolute numeric pattern points to a position within the string when the beginning of the string is position 1.

   The string is divided into two substrings.

   • The first substring extends from the beginning of the string and up to, but not including, the position that corresponds to the numeric pattern and it is parsed using the variables named in the template before the pattern.
   • If the absolute numeric pattern specifies a position beyond the length of the string, it is readjusted to the first position beyond the length of the string and the entire string is parsed using the variables named in the template before the pattern.
4. Relative numeric pattern

   The relative numeric pattern (a signed number) specifies a position within the string, relative to the last position.

5. Last position

   It is the beginning of the string when the relative numeric pattern is the first pattern in the template.

   • If the relative numeric pattern is not the first pattern in the template and the previous pattern was numeric, the last position is that specified by the previous numeric pattern.
   • If the relative numeric pattern is not the first pattern in the template and the previous pattern was a string, the last position is that of the starting character of the match (if there was a match) or the position following the end of the string (if there was no match).

As a result of what was just explained:

• If a pattern was not matched until the end of the string and the following pattern is a string pattern, this new string pattern is ignored since the starting point for the new scan is the end of the string.
• If a pattern was not matched until the end of the string and the following pattern is a numeric pattern, then the scan and subsequent parsing will resume from the new position indicated by that numeric pattern.

  Example 1

A parsing template with two absolute numeric patterns (with the second position preceding the first):

The following DO SET statements:

DO SET=%%S = THIS IS A SAMPLE STRING

DO SET=%%T = A1 A2 11 A3 6 A4

DO SET=%%$PARSE %%S %%T

have the same result as the following DO SET statements:

DO SET=%%A1 = THIS

DO SET=%%A2 = IS A

DO SET=%%A3 = SAMPLE STRING

DO SET=%%A4 = IS A SAMPLE STRING

• First substring: THIS IS A (up to, not including, position 11)

  As a result of parsing:

  A1=THIS
A2=IS A

• Second substring: SAMPLE STRING (from position 11 and up to the end of the string; since the next pattern, position 6, precedes the previous position, it cannot limit this second substring)

  As a result of parsing:

  A3=SAMPLE STRING

• Third substring: IS A SAMPLE STRING (from position 6 and to the end of the string)

  As a result of parsing:

  A4=IS A SAMPLE STRING

  Example 2

A parsing template with one absolute and one relative numeric pattern:

DO SET=%%S = THIS IS A SAMPLE STRING

DO SET=%%T = A1 6 A2 +3 A3

DO SET=%%$PARSE %%S %%T

• First substring: THIS (beginning of the string up to, but not including, position 6).

  As a result of parsing:

  A1=THIS

• Second substring: IS (from position 6 up to, but not including, position 6+3=9)

  As a result of parsing

  A2=IS

• Third substring: A SAMPLE STRING (from position 9 to the end of the string)

  As a result of parsing:

  A3=A SAMPLE STRING

  Example 3

A parsing template with two relative numeric patterns:

The following DO SET statements

DO SET=%%T = A1 A2 +40 A3 -13 A4 A5

DO SET=%%S = THIS IS A SAMPLE STRING

DO SET=%%$PARSE %%S %%T

have the same result as the following DO SET statements:

DO SET=%%A1 = THIS

DO SET=%%A2 = IS A SAMPLE STRING

DO SET=%%A3 = %%NULL

DO SET=%%A4 = SAMPLE

DO SET=%%A5 = STRING

The first numeric pattern specifies a position at column 40. This is beyond the end of the string so the position is reset to column 24 (end of the string + 1). As a result, the whole string is parsed to words using the A1 and A2 variables.

The second numeric pattern specifies a position at column 11 (end of the string + 1 minus 13) that precedes the position (40 readjusted to 24) previously specified; therefore the data from the last position (which is the end of the string) to the end of the string is parsed to words using the A3 variable (A3 is set to NULL).

The data (from column 12 to the end of the string) is parsed to words using the A4 and A5 variables.

Example 4

Combining a string pattern and numeric pattern

The following DO SET statements

DO SET=%%S = THIS IS A SAMPLE STRING

DO SET=%%T = A1 'A' A2 +3 A3

DO SET=%%$PARSE %%S %%T

have the same result as the following DO SET statements:

DO SET=%%A1 = THIS IS

DO SET=%%A2 = A S

DO SET=%%A3 = AMPLE STRING

The pattern specifies a string (A) that is matched at column 9. The data before column 9 is parsed to words using the A1 variable. The Numeric pattern (+3) specifies a position at column 12 by using relative position. The data from column 9 to column 12 is parsed to words using the A2 variable. The remaining data (from column 12 to the end of the string) is parsed to words using the A3 variable.