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Parallelizing diff Filter

Back in 1992, after I left Digital Equipment and VMS and found myself programming on Suns and PCs, I wrote this utility to take the output of diff and display it in a parallel (side-by-side) format, emulating the /PARALLEL option on the VMS version of diff. Once you get used to side-by-side diff output, you really never want to go back.

The code was developed on a Sun workstation. I soon thereafter ported it to DOS. Most recently, I have moved it to Linux. I used KDevelop in order to quickly bring up the automake/autoconf environment.

It has come to my attention that GNU diff has a --side-by-side option. I must admit that I don't understand this option too well, but, for the curious, pardiff output is different. Pardiff surrounds each diff section (called a hunk in GNU diff terminology) with dashes and pipe characters, includes line numbers with each section, and will truncate diff lines in order to format the output to the terminal. Pardiff's output format is not my invention, but simply an emulation of DIFF/PARALLEL on VMS.


Pardiff detects the width of the terminal on which it is running and adjusts its output accordingly.


Pardiff has no options. Simply pipe the output of diff to it. E.g.:
$ diff file1 file2 | pardiff | more

The distribution includes a shell script ("diffp") to do the above (I generally alias it to "dp").

To display context output format diff in a side-by-side mode, use the -C option, e.g.:

$ diff -C3 file1 file2 | pardiff -C | more

Screen shots

Everybody else does them... so... here's pardiff in action.


Pardiff is licensed under the GNU General Public License.


Pardiff has been compiled on Red Hat Linux 6.0 through 7.1, Solaris 7 for Intel, HP-UX 10.20, NetBSD, FreeBSD and OpenBSD. The source code is nearly identical to the version which compiled both on the Sun workstation (in 1992) and DOS. I expect that it will be easy to get it to compile in any ANSI C environment, but the terminal width detection code is UNIX-only, I believe.

If you successfully compile pardiff on other platforms, please let me know.

Bugs and Limitations

Pardiff has a fixed width in the display for line numbers, and therefore file line numbers with 6 or more characters throw off the formatting.

TABs and other control characters may throw off the formatting.



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