ARCH(1)                   BSD General Commands Manual                  ARCH(1)

NAME
     arch -- print architecture type or run selected architecture of a univer-
     sal binary

SYNOPSIS
     arch
     arch [-32] [-64] [[-arch_name | -arch arch_name]...] [-c] [-d envname]...
          [-e envname=value]... [-h] prog [args ...]

DESCRIPTION
     The arch command with no arguments, displays the machine's architecture
     type.

     The other use of the arch command it to run a selected architecture of a
     universal binary.  A universal binary contains code that can run on dif-
     ferent architectures.  By default, the operating system will select the
     architecture that most closely matches the processor type.  This means
     that an intel architecture is selected on intel processors and a powerpc
     architecture is selected on powerpc processors.  A 64-bit architecture is
     preferred over a 32-bit architecture on a 64-bit processor, while only
     32-bit architectures can run on a 32-bit processor.

     When the most natural architecture is unavailable, the operating system
     will try to pick another architecture.  On 64-bit processors, a 32-bit
     architecture is tried.  If this is also unavailable, the operating system
     on an intel processor will try running a 32-bit powerpc architecture.
     Otherwise, no architecture is run, and an error results.

     The arch command can be used to alter the operating system's normal
     selection order.  The most common use is to select the 32-bit architec-
     ture on a 64-bit processor, even if a 64-bit architecture is available.

     The arch_name argument must be one of the currently supported architec-
     tures:

           i386    32-bit intel

           x86_64  64-bit intel

     Either prefix the architecture with a hyphen, or (for compatibility with
     other commands), use -arch followed by the architecture.

     If more than one architecture is specified, the operating system will try
     each one in order, skipping an architecture that is not supported on the
     current processor, or is unavailable in the universal binary.

     The other options are:

     -32               Add the native 32-bit architecture to the list of
                       architectures.

     -64               Add the native 64-bit architecture to the list of
                       architectures.

     -c                Clears the environment that will be passed to the com-
                       mand to be run.

     -d envname        Deletes the named environment variable from the envi-
                       ronment that will be passed to the command to be run.

     -e envname=value  Assigns the given value to the named environment vari-
                       able in the environment that will be passed to the com-
                       mand to be run.  Any existing environment variable with
                       the same name will be replaced.

     -h                Prints a usage message and exits.

     The prog argument is the command to run, followed by any arguments to
     pass to the command.  It can be a full or partial path, while a lone name
     will be looked up in the user's command search path.

     If no architectures are specified on the command line, the arch command
     takes the basename of the prog argument and searches for the first prop-
     erty list file with that basename and the .plist suffix, in the
     archSettings sub-directory in each of the standard domains, in the fol-
     lowing order:

           ~/Library/archSettings         User settings

           /Library/archSettings          Local settings

           /Network/Library/archSettings  Network settings

           /System/Library/archSettings   System settings

     This property list contains the architecture order preferences, as well
     as the full path to the real executable.  For examples of the property
     list format, look at the files in /System/Library/archSettings.

   Example
     On an intel processor:

           % perl -MConfig -e 'printf "%s\n", $Config{byteorder}'
           1234

     shows the intel little endian byte order.

   Making links to the arch command
     When a link is made to arch command with a different name, that name is
     used to find the corresponding property list file.  Thus, other commands
     can be wrapped so that they have custom architecture selection order.

     Because of some internal logic in the code, hard links to the arch com-
     mand may not work quite right.  It is best to avoid using hard links, and
     only use symbolic links to the arch command.

   Environment
     The environment variable ARCHPREFERENCE can be used to provide architec-
     ture order preferences.  It is checked before looking for the correspond-
     ing property list file.

     The value of the environment variable ARCHPREFERENCE is composed of one
     or more specifiers, separated by semicolons.  A specifier is made up of
     one, two or three fields, separated by colons.  Architectures specified
     in order, are separated by commas and make up the last (mandatory) field.
     The first field, if specified, is a name of a program, which selects this
     specifier if that name matches the program name in question.  If the name
     field is empty or there is no name field, the specifier matches any pro-
     gram name.  Thus, ordering of specifiers is important, and the one with
     no name should be last.

     When the arch command is called directly, the prog name provides the path
     information to the executable (possibly via the command search path).
     When a name is specified in a ARCHPREFERENCE specifier, the path informa-
     tion can alternately be specified as a second field following the name.
     When the arch command is called indirectly via a link, this path informa-
     tion must be specified.  If not specified as a second field in a speci-
     fier, the executable path will be looked up in the corresponding property
     list file.

   Example ARCHPREFERENCE Values
     i386,x86_64
           A specifier that matches any name.

     foo:i386,x86_64
           A specifier that matches the program named foo (the full executable
           path is in the foo.plist file).

     foo:/op/bin/boo:i386,x86_64
           A specifier with all fields specified.

     baz:i386;x86_64
           A specifier for baz and a second specifier that would match any
           other name.

BUGS
     Running the arch command on an interpreter script may not work if the
     interpreter is a link to the arch command, especially if a 64-bit archi-
     tecture is specified (since the arch command is 2-way universal, 32-bit
     only).

SEE ALSO
     machine(1)

Mac OS X                         July 8, 2010                         Mac OS X