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 [-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 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 -h option prints a usage message and exits.
The arch_name argument must be one of the currently supported architec-
tures:
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 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, 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 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
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 archi-
tecture 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
Mac OS X 10.6 - Generated Thu Sep 17 20:07:09 CDT 2009