diff

compare files

• side-by-side comparison: diff -y file1 file2
• unified format: diff -u file1 file2
• ignore whitespace differences: diff -w file1 file2

merge files

vimdiff

• Use dp (put changes) and do (get changes) to merge

vimdiff file1 file2

• sometimes, vimdiff copies more than you want, try the following:

:diffget . 
#:diffput .

if you get more than one match for ., mark the whole line with v and use :diffget

sdiff

• step-by-step side-by-side merging:

sdiff -o mergedfile file1 file2