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ARCH(1) BSD General Commands Manual ARCH(1)
NAME
arch -- print architecture type or run selected architecture of a universal binary
SYNOPSIS
arch
arch [-h] [[-arch_name | -arch arch_name]...] 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 different architectures. By default, the operating system will
select the architecture that most closely matches the processor type. This means that an intel archi-tecture architecture
tecture 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 archi-tecture. architecture.
tecture. On 64-bit processors, a 32-bit architecture is tried. If this is also unavailable, the oper-ating operating
ating 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 architecture on a 64-bit processor, even if a 64-bit architecture is avail-able. available.
able.
The -h option prints a usage message and exits.
The arch_name argument must be one of the currently supported architectures:
i386 32-bit intel
ppc 32-bit powerpc
ppc64 64-bit powerpc
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 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. 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, while:
% arch -ppc perl -MConfig -e 'printf "%s\n", $Config{byteorder}'
4321
runs the powerpc architecture, and displays big 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 selec-tion selection
tion 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 pro-gram program
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 information can alternately be specified as a second field following the name. When the arch com-mand command
mand 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.
Example ARCHPREFERENCE Values
ppc,i386,ppc64,x86_64
A specifier that matches any name.
foo:ppc,i386,ppc64,x86_64
A specifier that matches the program named foo (the full executable path is in the foo.plist
file).
foo:/op/bin/boo:ppc,i386,ppc64,x86_64
A specifier with all fields specified.
baz:ppc,i386;i386,ppc
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 architecture is specified (since the arch command is 2-way universal,
32-bit only).
SEE ALSO
machine(1)
Mac OS X November 12, 2006 Mac OS X
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