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deepmind.google·6d ago
AI Engineering
Lobsters·Jun 30·5 min read
Platform Support for GNU Extensions to Basic Regular Expressions
TL;DR
A misunderstanding arose regarding the use of the '+' character in basic regular expressions (BREs) versus extended regular expressions (EREs). Testing on FreeBSD revealed that the '\+' character is a GNU extension that allows for one or more repetitions in BREs.
✦ Why It Matters
Understanding the differences in regular expression implementations can prevent errors in cross-platform scripting.
Key Takeaways
- Verify regular expression compatibility across different platforms.
- Use GNU extensions cautiously in scripts for portability.
- Consult documentation for specific regular expression behaviors.
- Test regular expressions in the target environment before deployment.
Full Summary
Basic regular expressions (BREs) and extended regular expressions (EREs) are two different syntaxes used in pattern matching. A colleague's shell script used the syntax '\+' to denote one or more repetitions, which led to confusion about its validity in BREs.
To investigate, a FreeBSD virtual machine was set up to test this syntax, confirming that '\+' works as intended. However, it was found that this behavior is a GNU extension and not included in the POSIX specification, which leaves its implementation open to interpretation.
The POSIX specification states that the behavior of certain characters, including '?', '+', and '|', is implementation-defined. This distinction is crucial for developers to understand when writing scripts that may run on different systems.
Knowing the differences between BREs and EREs can help avoid compatibility issues in cross-platform scripting.