How do I convert between Unix and Mac OS or Mac OS X text files?

Traditionally, Unix and Mac OS differ in the format in which they store text files. Mac OS places a carriage return character at the end of each line of a text file, but Unix uses a line feed character. Some Unix applications won't recognize the carriage returns added by Mac OS, and will display a file as a single line, interspersed with Ctrl-m characters. This appears on the screen as ^M. Similarly, some Mac OS applications need to see carriage return characters at the ends of lines, and may treat Unix-format files as one long line.

In Mac OS X, the situation is more complicated. Because Mac OS X is a meld of Unix and the older Mac OS, in some cases text files have carriage returns and in others they have line feeds. For the most part, classic applications still require text files to have carriage returns, while the command-line Unix utilities require line feeds. Mac OS X-native applications are frequently capable of interpreting both.

There are many ways to resolve the differences in format. In this document you will find instructions on how to use Transmit, MacSFTP, Fetch, command-line FTP, tr, awk, and Perl to do the conversion. In Mac OS 9.x and earlier, before using these utilities, the files you are converting must first be on a Unix computer, unless you are using Transmit or Fetch, in which case the files must first be on a Macintosh. In Mac OS X, you may use all of these methods from your own computer; use Transmit, MacSFTP, and Fetch normally, and command-line FTP, tr, awk, and Perl from the Terminal application.

Transmit

When using Transmit to move a text file between Unix and Mac OS, be sure to transfer the file in ASCII mode. This will ensure that the document is transformed into a text format appropriate for the host. Normally, Transmit will automatically decide what mode to transfer a file in; to force it to transfer files as text, from the File menu, select ASCII Mode.

MacSFTP

When using MacSFTP to move a text file between Unix and Mac OS, be sure to translate the linefeeds. This will ensure that the document is transformed into a text format appropriate for the host. To do this, from the MacSFTP (Mac OS X) or Edit (Mac OS 9.x and earlier) menu, select Preferences... . In the preferences window, click the File Transfer tab, then check the box next to Translate text files linefeeds. Click Save to apply the setting change.

Fetch

When using Fetch to move a text file between Unix and Mac OS, be sure to transfer the file while Fetch is in Text mode. This will ensure that the document is transformed into a text format appropriate for the host. The format is specified by three buttons that appear in the Fetch window after a connection has been made. To force a file to be transferred in the Text mode, select Text in the "Format:" pop-up menu (Fetch 4) or click the Text button (Fetch 3 and earlier) before transferring.

Typically, Automatic mode is selected by default; in this mode, Fetch tries to determine whether a file is a binary or text file by looking up the extension of the file in its suffix mapping list. This list can be examined and modified by going to the Customize menu and selecting Suffix Mapping. If Fetch cannot find the file's extension in the list (or if the file has no extension at all), it will default to either Text mode or Binary mode, depending on the setting under the Customize menu, in Preferences.

Command-line FTP

When using command-line FTP to move a text file between Unix and Mac OS, be sure to transfer the file in ASCII format. This will ensure that the document is transformed into a text format appropriate for the host. To do so, before you begin the file transfer, at the FTP prompt, enter:

ascii

`tr`

The Unix program tr is used to translate between two sets of characters. Characters specified in one set are converted to the matching character in the second set. Thus, to convert the Ctrl-m of a Mac OS text file to the line feed (Ctrl-j) of a Unix text file, at the Unix command line, enter:

tr '\r' '\n' < macfile.txt > unixfile.txt

Here, \r and \n are special escape sequences that tr interprets as Ctrl-m (a carriage return) and Ctrl-j (a line feed), respectively. Thus, to convert a Unix text file to a Mac OS text file, enter:

tr '\n' '\r' < unixfile.txt > macfile.txt

Note: The escape sequences must be surrounded by single quotation marks for these commands to work.

`awk`

To use awk to convert a Mac OS file to Unix, at the Unix prompt, enter:

awk '{ gsub("\r", "\n"); print $0;}' macfile.txt > unixfile.txt

To convert a Unix file to Mac OS using awk, at the command line, enter:

awk '{ gsub("\n, "\r"); print $0;}' unixfile.txt > macfile.txt

On some systems, the version of awk may be old and not include the function gsub. If so, try the same command, but replace awk with gawk or nawk.

Perl

To convert a Mac OS text file to a Unix text file using Perl, at the Unix shell prompt, enter:

perl -p -e 's/\r/\n/g' < macfile.txt > unixfile.txt

To convert from a Unix text file to a Mac OS text file with Perl, at the Unix shell prompt, enter:

perl -p -e 's/\n/\r/g' < unixfile.txt > macfile.txt

Note: You must use single quotation marks in either command line. This prevents your shell from trying to evaluate anything inside the quotation marks. At Indiana University, Perl is installed on all UITS shared central Unix systems.

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Last modified on May 15, 2005.

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