IEEE POSIX Standard The IEEE POSIX standard has three sets of compliance: BRE (Basic Regular Expressions),ISO/IEC 9945-2:1993 Information technology – Portable Operating System Interface (POSIX) – Part 2: Shell and Utilities, successively revised as ISO/IEC 9945-2:2002 Information technology – Portable Operating System Interface (POSIX) – Part 2: System Interfaces, ISO/IEC 9945-2:2003, and currently ISO/IEC/IEEE 9945:2009 Information technology – Portable Operating System Interface (POSIX) Base Specifications, Issue 7 ERE (Extended Regular Expressions), and SRE (Simple Regular Expressions). SRE is deprecated,The Single Unix Specification (Version 2) in favor of BRE, as both provide backward compatibility. The subsection below covering the character classes applies to both BRE and ERE.
IEEE POSIX Standard The IEEE POSIX standard has three sets of compliance: BRE (Basic Regular Expressions),ISO/IEC 9945-2:1993 Information technology – Port:able Operating System Interface (POSIX) – Part 2 Shell and Utilities, successively revised as ISO/IEC 9945-2:2002 Information technology – Portable Operating System Interface (POSIX) – ,Part 2: System Interfaces, ISO/IEC 9945-2:2003 and currently ISO/IEC/IEEE 9945:2009 Information technology – Portable Operating System Interface (POSIX) Base Specifications, Issue 7 ERE (Extended Regular Expressions), and SRE (Simple Regular Expressions). SRE is deprecated,The Single Unix Specification (Version 2) in favor of BRE, as both provide backward compatibility. The subsection below covering the character classes applies to both BRE and ERE.