use v5.40;subfoo;my$pat =qr/^(?:a|aa)(*{foo(substr$_, pos)})(*F)/;subfoo($x) {say$x ||'- fin -';$x =~/$pat/;}foo'aaaaaaaa';

Summary of my perl5 (revision 5 version 40 subversion 0) configuration:     Platform:    osname=linux    osvers=5.12.15-arch1-1    archname=x86_64-linux-thread-multi    uname='archlinux'    config_args='-des -Dusethreads -Duseshrplib -Doptimize=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions         -Wp,-D_FORTIFY_SOURCE=3 -Wformat -Werror=format-security         -fstack-clash-protection -fcf-protection         -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -ffile-prefix-map=/build/perl/src=/usr/src/debug/perl -flto=auto -Dprefix=/usr -Dvendorprefix=/usr -Dprivlib=/usr/share/perl5/core_perl -Darchlib=/usr/lib/perl5/5.40/core_perl -Dsitelib=/usr/share/perl5/site_perl -Dsitearch=/usr/lib/perl5/5.40/site_perl -Dvendorlib=/usr/share/perl5/vendor_perl -Dvendorarch=/usr/lib/perl5/5.40/vendor_perl -Dscriptdir=/usr/bin/core_perl -Dsitescript=/usr/bin/site_perl -Dvendorscript=/usr/bin/vendor_perl -Dinc_version_list=none -Dman1ext=1perl -Dman3ext=3perl -Dlddlflags=-shared -Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now          -Wl,-z,pack-relative-relocs -flto=auto -Dldflags=-Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now          -Wl,-z,pack-relative-relocs -flto=auto -Dloclibpth=/usr/lib/db5.3 -Dlocincpth=/usr/include/db5.3'    hint=recommended    useposix=true    d_sigaction=define    useithreads=define    usemultiplicity=define    use64bitint=define    use64bitall=define    uselongdouble=undef    usemymalloc=n    default_inc_excludes_dot=define  Compiler:    cc='cc'    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/include/db5.3 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'    optimize='-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=3 -Wformat -Werror=format-security -fstack-clash-protection -fcf-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -ffile-prefix-map=/build/perl/src=/usr/src/debug/perl -flto=auto'    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/include/db5.3'    ccversion=''    gccversion='14.2.1 20240805'    gccosandvers=''    intsize=4    longsize=8    ptrsize=8    doublesize=8    byteorder=12345678    doublekind=3    d_longlong=define    longlongsize=8    d_longdbl=define    longdblsize=16    longdblkind=3    ivtype='long'    ivsize=8    nvtype='double'    nvsize=8    Off_t='off_t'    lseeksize=8    alignbytes=8    prototype=define  Linker and Libraries:    ld='cc'    ldflags ='-Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now -Wl,-z,pack-relative-relocs -flto=auto -fstack-protector-strong -L/usr/lib/db5.3'    libpth=/usr/local/lib /usr/lib /usr/lib/db5.3    libs=-lpthread -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc    libc=/lib/../lib/libc.so.6    so=so    useshrplib=true    libperl=libperl.so    gnulibc_version='2.40'  Dynamic Linking:    dlsrc=dl_dlopen.xs    dlext=so    d_dlsymun=undef    ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.40/core_perl/CORE'    cccdlflags='-fPIC'    lddlflags='-shared -Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now -Wl,-z,pack-relative-relocs -flto=auto -L/usr/lib/db5.3 -fstack-protector-strong'Characteristics of this binary (from libperl):   Compile-time options:    HAS_LONG_DOUBLE    HAS_STRTOLD    HAS_TIMES    MULTIPLICITY    PERLIO_LAYERS    PERL_COPY_ON_WRITE    PERL_DONT_CREATE_GVSV    PERL_HASH_FUNC_SIPHASH13    PERL_HASH_USE_SBOX32    PERL_MALLOC_WRAP    PERL_OP_PARENT    PERL_PRESERVE_IVUV    PERL_USE_SAFE_PUTENV    USE_64_BIT_ALL    USE_64_BIT_INT    USE_ITHREADS    USE_LARGE_FILES    USE_LOCALE    USE_LOCALE_COLLATE    USE_LOCALE_CTYPE    USE_LOCALE_NUMERIC    USE_LOCALE_TIME    USE_PERLIO    USE_PERL_ATOF    USE_REENTRANT_API    USE_THREAD_SAFE_LOCALE  Built under linux  Compiled at Sep  1 2024 11:21:17  @INC:    /usr/lib/perl5/5.40/site_perl    /usr/share/perl5/site_perl    /usr/lib/perl5/5.40/vendor_perl    /usr/share/perl5/vendor_perl    /usr/lib/perl5/5.40/core_perl    /usr/share/perl5/core_perl