Reference Implementations Test Data Repository Usage Reference Implementation Notes testregex Notes

AT&T Research regex(3) regression tests

Glenn Fowler <>

AT&T Research - Florham Park NJ

testregex.c 2004-05-31 is the latest source for the AT&T Research regression test harness for the X/Open regex pattern match interface. See testregex(1) for option and test input details. The source and test data posted here are license free.

testregex can:

  • verify stability for a particular implementation in the face of source code and/or compilation environment changes
  • verify standard compliance for all implementations
  • provide a basis for discussions on what compliance means

See An Interpretation of the POSIX regex Standards for an analysis of the POSIX-X/Open regex standards.

Reference Implementations

testregex is currently built against these reference implementations:

AT&T ast    A    Glenn Fowler and Doug McIlroy
bsd    B     
Bell Labs    D    Doug McIlroy
old gnu    G     
gnu    H    Isamu Hasegawa
irix    I     
boost    J    John Maddock
regex++    M    John Maddock
pcre perl compatible    P    Philip Hazel
rx    R    Tom Lord
spencer    S    Henry Spencer
libtre    T    Ville Laurikari
unix caldera    U     

Test Data Repository

basic.dat      basic regex(3) -- all implementations should pass these
categorize.dat      implementation categorization
nullsubexpr.dat      null (...)* tests
leftassoc.dat      left associative catenation implementation must pass these
rightassoc.dat      right associative catenation implementation must pass these
forcedassoc.dat      subexpression grouping to force associativity
repetition.dat      explicit vs. implicit repetitions


To run the basic.dat tests:
testregex < basic.dat

If the local implementation hangs or dumps on some tests then run with the -c option. The -h option lists the test data format details. The test data files exercise all features; the test harness detects and ignores features not supported by the local implementation.

Reference Implementation Notes

D: diet libc

The diet libc implementation is currently omitted because it fails all but one basic.dat test.


The P implementation emulates perl(1) and is not X/Open compliant by design. The main differences are:
  • P leftmost-first matching as opposed to the X/Open leftmost-longest.
  • REG_EXTENDED patterns only.

However, the P package regression tests, and perl(1) features creeping into other implementations, make it reasonable to include here.

testregex Notes

Extensions to the standard terminology are derived from the AT&T implementation, unified under <regex.h> with these modes:

BRE    0    basic RE
ERE    REG_EXTENDED    egrep RE with perl (...) extensions
ARE    REG_AUGMENTED    ERE with ! negation, <> word boundaries
SRE    REG_SHELL    sh patterns
KRE    REG_SHELL|REG_AUGMENTED    ksh93 patterns: ! @ ( | & ) { }
LRE    REG_LITERAL    fgrep patterns

and a few flags to handle fnmatch(3):

regex FLAG    fnmatch FLAG

The original testregex.c was done by Doug McIlroy at Bell Labs. The current implementation is maintained by Glenn Fowler <>.

Glenn Fowler
Information and Software Systems Research
AT&T Labs Research
Florham Park NJ
March 22, 2011