arch(1) man page

ARCH(1) General Commands Manual ARCH(1)

NAME
arch – print architecture type or run selected architecture of a
universal 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 is to run a selected architecture of a
universal binary. A universal binary contains code that can run on
different architectures. By default, the operating system will select
the architecture that most closely matches the processor type. 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. 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
architecture on a 64-bit processor, even if a 64-bit architecture is
available.

The arch_name argument must be one of the currently supported
architectures:

i386 32-bit intel

x86_64 64-bit intel

x86_64h 64-bit intel (haswell)

arm64 64-bit arm

arm64e 64-bit arm (Apple Silicon)

If the binary does not contain code for arch_name, the arch command may
try to select a close match. If arm64 is specified and not found, arm64e
will be tried next. If this happens, the order the architectures will be
tried is not guaranteed.

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
command to be run.

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

-e envname=value Assigns the given value to the named environment
variable in the environment that will be passed
to the command 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
property list file with that basename and the .plist suffix, in the
archSettings sub-directory in each of the standard domains, in the
following 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. Please refer to the EXAMPLES
section for an example of the property list file format.

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
command 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
architecture order preferences. It is checked before looking for the
corresponding 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
program 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
information can alternately be specified as a second field following the
name. When the arch command is called indirectly via a link, this path
information must be specified. If not specified as a second field in a
specifier, the executable path will be looked up in the corresponding
property list file.

EXAMPLES
archSettings Property List Format
This is an example of a property list file as is expected in one of the
archSettings locations mentioned above:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>ExecutablePath</key>
<string>$execpath</string>
<key>PreferredOrder</key>
<array>
<string>x86_64</string>
<string>arm64</string>
</array>
<key>PropertyListVersion</key>
<string>1.0</string>
</dict>
</plist>

ARCHPREFERENCE Values
i386,x86_64,x86_64h,arm64,arm64e
A specifier that matches any name.

foo:i386,x86_64,x86_64h,arm64,arm64e
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,x86_64h,arm64,arm64e
A specifier with all fields specified.

baz:i386;x86_64,x86_64h,arm64,arm64e
A specifier for baz and a second specifier that would match any
other name.