On OS X, how do I find out what architecture a shared lib is compiled for?

I need to know whethe开发者_高级运维r I compiled libjpeg for 32 or 64 bits architecture, but don't know how to find out, is there a command that will let me check?

just type file libjpeg.dylib and you'll get output like the following

libpoll.dylib: Mach-O universal binary with 3 architectures
libpoll.dylib (for architecture x86_64): Mach-O 64-bit dynamically linked shared library x86_64
libpoll.dylib (for architecture i386): Mach-O dynamically linked shared library i386
libpoll.dylib (for architecture ppc7400): Mach-O dynamically linked shared library ppc

The file command will work just fine. Alternatively, you can use otool to print the fat headers.

$ otool -vf /usr/lib/libSystem.B.dylib
Fat headers
fat_magic FAT_MAGIC
nfat_arch 2
architecture ppc
    cputype CPU_TYPE_POWERPC
    cpusubtype CPU_SUBTYPE_POWERPC_ALL
    offset 4096
    size 2221800
    align 2^12 (4096)
architecture ppc64
    cputype CPU_TYPE_POWERPC64
    cpusubtype CPU_SUBTYPE_POWERPC64_ALL
    offset 2228224
    size 2169980
    align 2^12 (4096)

Use the file command:

[mqudsi@iqudsi:Xcode/FSLogger]$ file ./original                   (07-31 02:53)
./original: Mach-O executable i386