In a large software system it is often very useful to be able keep record, file and table descriptions in a central source text library and then to import those descriptions into the programs that require them. In COBOL the COPY verb allows us to do this.

This unit introduces the COPY verb.

It describes some problems of large software systems which use of the COPY helps to alleviate.

It introduces the syntax of the COPY verb and discusses how the COPY verb, and in particular how COPY..REPLACING, works.

It introduces the notion of a text word and describes the role that these play in matching the text in the REPLACING phrase with the text in the library file.

The unit ends with a number of example programs.

By the end of this unit you should -

1. Be aware of some of the advantages of using the COPY verb.
2. Understand what a text word and be able to identify text words in library text.
3. Be able to use the COPY.. REPLACING to copy source text from a library file and replace sections of it as required.

• Introduction to COBOL
• Declaring data in COBOL
• Basic Procedure Division commands
• Selection in COBOL
• Iteration in COBOL
• Introduction to Sequential files
• Processing Sequential files
• Edited Pictures
• The USAGE clause
• COBOL print files and variable-length records
• Sorting and Merging
• Introduction to direct access files
• Relative Files
• Indexed Files
• Using tables
• Creating tables - syntax and semantics
• Searching tables
• CALLing subprograms

COPY statements in a COBOL program are very different from other COBOL statements. While other statements are executed at run time, COPY statements are executed at compile time.

A COPY statement is similar to the "Include" used in languages like C and C++. It allows programs to include frequently used source code text.

When a COPY statement is used in a COBOL program the source code text is copied into the program from a copy file or from a copy library before the program is compiled.

A copy file, is a file containing a segment of COBOL code.

A copy library, is a collection of code segments each of which can be referenced using a name. Each program that wants to use items described in the copy library uses the COPY verb to include the descriptions it requires.

When COPY statements include source code in a program, the code can be included without change or the text can be changed as it is copied into the program. The ability to change the code as it being included greatly adds to the versatility of the COPY verb.

The COPY verb is generally used when creating large software systems. These systems are subject to a number of problems that the COPY verb helps to alleviate.

For instance, when data files are used by a number of programs in a large software system, it is easy for programmers describing those files to make errors in defining the key fields (Indexed files) or the file organization or the type of access allowed or the number, type and size of the fields in a record. Any errors in these descriptions may result in difficult-to-find bugs. For instance, if one program writes a file using an incorrect record description and the others read it using the correct description, a program crash may occur in in one of the correct subprograms rather than the one which actually has the problem.

Using copy libraries or files helps to reduce programmer transcription errors and also makes implementation simpler by reducing the amount of coding required. For instance, when a number of programs need to access the same file, the relevant file and record descriptions can be copied from a copy library instead of each programmer having to type their own (and possibly get them wrong).

Another advantage of using copy libraries is that they permit item descriptions such as file, record and table descriptions, to be kept and updated centrally in a copy library, often under the control of a copy librarian. This makes it more difficult for programmers to make ad hoc changes to file and record formats. Such changes generally have to be approved by the COPY librarian.

In a large software system using the COPY verb makes some maintenance tasks easier and safer. Certain changes may only require an update to the text in the copy library and a recompilation of any affected programs. If a copy library were not used each affected program would have to be changed

Text Words

The matching procedure in the REPLACING phrase operates on text words.

A text word is defined as:

If the REPLACING phrase is not used the compiler simply copies the text into the client program without change.

If the COPY does use the REPLACING phrase the text is copied and each occurrence of TextWord1 in the library text is replaced by the corresponding TextWord2 in the REPLACING phrase.

Some example COPY statements

COPY CopyFile2 REPLACING XYZ BY 120.
COPY CopyFile5 REPLACING X(3) BY X(19).
COPY CopyFile3 IN EGLIB.
COPY CopyFile5 REPLACING ==X(3)== BY ==X(19)==.
COPY CopyFile4 IN EGLIB.

The REPLACING phrase tries to match the TextWord1 items with text words in the library text.If a match is achieved, then as the text is copied from the library, the matched text is replaced by the TextWord2 items.

For purposes of matching, each occurrence of aseparator comma, semicolon, space or comment line in the library text or in TextWord1 is considered to be a single space.

Each sequence of one or more space separators is also considered to be a single space.

Comment lines in the library text is or in TextWord2 are copied into the target text unchanged.

1. When TextWord1 is PseudoText it must not be null, nor can it consist solely of either the character space(s) or comment lines.
2. When TextWord2 is PseudoText it can be null. Null PseudoText is indicated by four equal signs (e.g. ====)
3. A COPY statement can occur anywhere a character-string or a separator can occur except that a COPY statement must not occur within another COPY statement.
4. TextName defines a unique external filename which conforms to the rules for user defined words.
5. If the word COPY appears in a comment-entry or in the place where a comment entry can appear, it is considered part of the comment-entry.
6. The text produced as a result of the complete processing of a COPY statement must not contain a COPY statement.
7. Normally a textword in the copy text is replaced by a textword in the replacement text but it is possible to replace only part of a text-word by enclosing the text to be replaced by either parentheses or colons.
   For example - (Prefix) or :Prefix: