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File Handling in MUMPS

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File handling is a crucial aspect of any programming language, allowing you to read from and write to files. In MUMPS, file handling is performed using a combination of built-in commands and functions. This section will cover the basics of file handling, including opening, reading, writing, and closing files.

Key Concepts

  1. File Operations: Understanding the basic operations such as opening, reading, writing, and closing files.
  2. File Modes: Different modes in which a file can be opened (e.g., read, write, append).
  3. Error Handling: Managing errors that may occur during file operations.

File Operations

Opening a File

To open a file in MUMPS, you use the OPEN command. The syntax is as follows:

OPEN fileName:(mode):timeout
  • fileName: The name of the file you want to open.
  • mode: The mode in which you want to open the file (e.g., "R" for read, "W" for write, "A" for append).
  • timeout: The time to wait if the file is not immediately available.

Example: Opening a File for Reading

OPEN "example.txt":"R":5
USE "example.txt"

Reading from a File

To read from a file, you use the READ command. The syntax is:

READ variable

Example: Reading a Line from a File

NEW line
READ line
WRITE line, !

Writing to a File

To write to a file, you use the WRITE command. The syntax is:

WRITE data

Example: Writing a Line to a File

OPEN "example.txt":"W":5
USE "example.txt"
WRITE "Hello, MUMPS!", !
CLOSE "example.txt"

Closing a File

To close a file, you use the CLOSE command. The syntax is:

CLOSE fileName

Example: Closing a File

CLOSE "example.txt"

Practical Example

Let's put it all together in a practical example where we read from one file and write its contents to another file.

Example: Copying File Contents

NEW line

; Open the source file for reading
OPEN "source.txt":"R":5
USE "source.txt"

; Open the destination file for writing
OPEN "destination.txt":"W":5
USE "destination.txt"

; Read from source and write to destination
FOR  DO  QUIT:$ZEOF
. READ line
. WRITE line, !

; Close both files
CLOSE "source.txt"
CLOSE "destination.txt"

Error Handling

Error handling is essential to manage any issues that may arise during file operations. MUMPS provides the $ZEOF special variable to check for the end of a file and $ZSTATUS to get the status of the last operation.

Example: Error Handling

NEW line

; Open the file for reading
OPEN "example.txt":"R":5
USE "example.txt"

; Read from the file with error handling
FOR  DO  QUIT:$ZEOF
. READ line
. IF $ZSTATUS'="" DO
. . WRITE "Error: ", $ZSTATUS, !
. ELSE  DO
. . WRITE line, !

; Close the file
CLOSE "example.txt"

Exercises

Exercise 1: Reading from a File

  1. Create a file named input.txt with the following content:

    Line 1
Line 2
Line 3

  2. Write a MUMPS program to read and display each line from input.txt.

Solution

NEW line

; Open the file for reading
OPEN "input.txt":"R":5
USE "input.txt"

; Read and display each line
FOR  DO  QUIT:$ZEOF
. READ line
. WRITE line, !

; Close the file
CLOSE "input.txt"

Exercise 2: Writing to a File

  1. Write a MUMPS program to write the following lines to a file named output.txt: 
    Hello, World!
Welcome to MUMPS.

Solution

; Open the file for writing
OPEN "output.txt":"W":5
USE "output.txt"

; Write lines to the file
WRITE "Hello, World!", !
WRITE "Welcome to MUMPS.", !

; Close the file
CLOSE "output.txt"

Conclusion

In this section, you learned the basics of file handling in MUMPS, including how to open, read, write, and close files. You also learned about error handling during file operations. These skills are essential for managing data stored in files and will be useful in more advanced programming tasks.

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