Thanks Ken and hv!

Using the raw numeric value worked! After opening the FILEHANDLE I added

fcntl($FI, 48, 1);

Which accomplished what I wanted. But I found the read performance to be much worse than expected. Also CPU usage went way up. Probably due to disk IO having to be managed more closely VS just buffering right into RAM.

So I will end up not using the F_NOCACHE for now. But good to know the option is available if I need it.

Thanks again!

Summary of my perl5 (revision 5 version 36 subversion 0) configuration
+:
   
  Platform:
    osname=darwin
    osvers=19.6.0
    archname=darwin-2level
    uname='darwin test-mac.local 19.6.0 darwin kernel version 19.6.0: 
+thu jan 13 01:26:33 pst 2022; root:xnu-6153.141.51~3release_x86_64 x8
+6_64 '
    config_args=''
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-fno-common -DPERL_DARWIN -mmacosx-version-min=10.15 -fn
+o-strict-aliasing -pipe -fstack-protector-strong -DPERL_USE_SAFE_PUTE
+NV'
    optimize='-O3'
    cppflags='-fno-common -DPERL_DARWIN -mmacosx-version-min=10.15 -fn
+o-strict-aliasing -pipe -fstack-protector-strong'
    ccversion=''
    gccversion='4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.32.62
+)'
    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 =' -mmacosx-version-min=10.15 -fstack-protector-strong'
    libpth=/Applications/Xcode.app/Contents/Developer/Toolchains/Xcode
+Default.xctoolchain/usr/lib/clang/11.0.3/lib /Applications/Xcode.app/
+Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sd
+k/usr/lib /Applications/Xcode.app/Contents/Developer/Toolchains/Xcode
+Default.xctoolchain/usr/lib /usr/lib
    libs=-lpthread -ldbm -ldl -lm -lutil -lc
    perllibs=-lpthread -ldl -lm -lutil -lc
    libc=
    so=dylib
    useshrplib=false
    libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=bundle
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags=' -mmacosx-version-min=10.15 -bundle -undefined dynamic_
+lookup -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_TIMES
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under darwin
  Compiled at Oct  7 2022 11:20:10
  @INC:
    /usr/local/lib/perl5/site_perl/5.36.0/darwin-2level
    /usr/local/lib/perl5/site_perl/5.36.0
    /usr/local/lib/perl5/5.36.0/darwin-2level
    /usr/local/lib/perl5/5.36.0

[download]

In reply to Re^2: macOS Fcntl.pm missing F_NOCACHE by bernuli
in thread macOS Fcntl.pm missing F_NOCACHE by bernuli

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