Filenames and pathnames differ among Unix, Windows, and Macintosh. Fortunately, Tcl is happy to work with Unix-style filenames internally. The file command provides help for dealing with filenames when you need to convert between the canonical form and forms required by specific operating systems. You will likely need a native filename if you exec programs that require filenames.

On Unix, the file command takes two or more file pathname components and joins them with the Tcl canonical path delimiter “/”:

file join /home tpoindex src tcl style.tcl

This code produces the following output:

/home/tpoindex/src/tcl/style.tcl

On Windows, the file command takes a pathname in canonical network form and returns the native pathname:

file nativename "/program files/tcl/bin/wish80.exe"

This code produces the following output:

program files	clinwish.exe

The file command has many other subcommands to delete, copy, and rename files in an operating system--independent fashion.

Unix, Windows, and Macintosh each have different end of line conventions for text files. In the default state, Tcl is very forgiving in reading files created on a different platform. When writing files to be used on a different system, you should configure the output channel by using the fconfigure command.

For example, if you are creating a file on Unix to be used primarily on a Windows system, use the following code:

set fd [open outfile w]
fconfigure $fd -translation crlf
puts $fd "hello windows!"

Tcl includes a preset array of platform-specific information named $tcl_platform. Elements are shown in the following table.

This information can be useful in deciding at runtime how to print a file, execute another program, and so forth.

Reading and writing binary data is always system dependent, especially native integer and floating-point values. The binary command provides character specifications to scan and format big- and little-endian 16- and 32-bit integers, machine- native single- and double-precision floating-point values, and other formats. The binary command uses format specifiers to determine what format data will be packed into, such as S to denote a 16-bit integer in big-endian^[7] order. The format s denotes a 16-bit integer in little-endian order. See the documentation for a complete list of specifiers. Here is a sample use of binary:

set binaryMsg [binary format SI 3 129];# 16 & 32-bit big endian
    ints

If you are scanning or formatting binary data for use by other programs on the same machine type, consult the endian order information in tcl_platform to choose the correct binary specification:

switch $tcl_platform(byteOrder) {
    littleEndian { set int32 i ; set int16 s }
    bigEndian    { set int32 I ; set int16 S }
}
binary scan $binaryMsg $int16$int32 messageNum messageCode

Note that the binary command does not have a specification character to scan unsigned integers. Signed integers can be converted to unsigned quantities with a simple expression. Consult the binary command manpages for more information.

# convert to 16 bit unsigned value
set messageNum [expr ($messageCode + 0x10000) % 0x10000]