Lecture 5

Strings and regular expressions

Lecture

Slides (PDF, PPTX).

Theory

• Strings in C
• Patterns
• Regular expressions

Workshop

Outline

• Practice using functions of the C language to handle strings
• Practice using Shell patterns and regular expressions
  • Shell
  • C language

Homework

Write a program that inputs three command-line arguments:

• argv[1] - regular expression;
• argv[2] - text;
• argv[3] - replacement.

The program finds all occurrences of the regular expression in the text and replaces all of them with the specified replacement string. The updated text is stored in a separate buffer and printed to the console in the end.

Hint: Algorithm is as follows. Allocate a buffer for the new text. Find a regular expression match. Copy to the buffer text before match. Copy to the buffer replacement. Find the next regular expression match and so on.

Note: The problem when the size of the allocated buffer is not enough to store the text can be solved by using the realloc function to allocated additional space.

References

• Jeffrey Friedl Mastering Regular Expressions (aka The Owl Book).
• regex101: build, test, and debug regex