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Examining Differences

16

This chapter further explains some features and presents an example of how to use Merging. The chapter is organized into the following sections:

Moving Between Differences

page 189

Resolving Differences

page 189

Automatic Merging

page 190

An Example

page 190

Moving Between Differences

You can navigate through differences using either the Next and Prev buttons or the up arrow and down arrows. Merging automatically moves to the next difference immediately after you resolve the current difference.

Resolving Differences

A difference is represented by a blank line in the merged (output) file in the lower text pane. To resolve a difference, you edit the line displayed there by either:

Automatic Merging

If you have loaded a common ancestor file, Merging is often able to resolve differences automatically, based on the following rules:

An Example

This example merges two files that have a common ancestor. The files are file_1 and file_2, and the ancestor file is named matriarch. The descendant files file_1 and file_2 were derived from matriarch by editing. The edits show all varieties of changes that could occur in the descendants: deleting lines, adding new lines, and changing lines.

The content of each line in the example helps to identify whether or not it was changed, and how. The ancestor file contains only twelve lines and is shown in Code Example 16-1.

Merging does not number lines in the files it loads; the numbers are part of the example text and were placed there for clarity.

Code  Example  16-1     Ancestor File (matriarch) 






1 This line is deleted in file_1





2 This line is in all three files





3 This line is deleted in file_2





4 This line is in all three files





5 This line is in all three files





6 This line is changed in descendants





7 This line is in all three files





8 This line is changed in descendants





9 This line is in all three files





10 This line is changed in file_2





11 This line is in all three files





12 This line is in all three files













 










Code Example 16-2 shows the contents of file_1. This file is identical to matriarch with the following exceptions: 




Code Example 16-3 shows the contents of file_2. This file is identical to matriarch with the following exceptions: 




To simplify the example, we place all three files in one directory, and use this directory as the working directory where we will start Merging.




 Starting Merging







  
Go to the directory in which matriarch, file_1, and file_2 are stored. 
Type the following to start Merging in background mode and load the 
three files:







demo% filemerge -a matriarch file_1 file_2 &







 










Merging starts up with the Auto Merge feature turned on by default. The window that appears displays an automerged output file. 



In the upper left of the window, Merging has reported finding seven differences, of which only one remains unresolved--six differences were resolved by automerging, and are marked by glyphs in outline font.



The meaning of the glyphs is as follows: a vertical bar means a change in the marked line, a plus sign signifies a line added, a minus sign means a line was deleted. Unresolved states are marked by solid glyphs, unresolved by outline. These glyphs are highlighted in color except when the color map is full. The default significance is: red indicates a change, green indicates a deletion, yellow shows an addition.



The unresolved difference (line 6) is marked by a vertical bar. 




 Examining Differences




Merging highlights the unresolved difference, which it identifies as the line numbered 6 in file_1 and file_2. When differences are being resolved with Merging, the resulting Merging window (filemerge.out) shows the current state of the file with automatic merging. 



Proceed to the next difference by choosing the down arrow above the appropriate file, or Navigate: Next Difference. The next difference becomes the current difference.



Proceed through the differences by clicking on the down arrow.



Auto Merge preserves a change that was made to one file if no change was made in the other file.



When a difference has not been resolved by Auto Merge, as indicated by the solid highlighted glyph next to the lines involved in the difference, you need to resolve the difference by making a choice. The vertical line indicates that the line has been changed (as opposed to added or deleted). In this case, Auto Merge failed because the same line was changed differently in the two files, and Merging could not decide which change was more valid.



You could resolve this difference in one of the following ways:





 Editing the Output File




To edit the output file, move the pointer into the output file's text pane and place it in the line you want to change. In this example, the following line was typed in:




>>> This line edited by hand <<<




Choose the Edit:Mark Selected as Resolved. This menu item marks the difference as resolved. In this example there are no more unresolved differences, so the next difference remains the current one.



Note that the message in the upper left part of the window now indicates that all differences have been resolved. Nevertheless, proceed to verify the automerged differences.



Continue through the differences by clicking on the down arrow. 



The final difference results from a line that was added only to file_2. Merging places the new line in the output file just as it did when a new line was added to file_1, which resulted in the third difference.




 Saving Output File




Now that all differences have been resolved and the automerged differences verified, you can save the output file. The output file takes the name shown in the Load Files pop-up window, which by default is filemerge.out.To write the file, choose Save from the File menu, or the Save button. To save the file under another name, use Save As, from the File menu.












 



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