What is the difference between Copied context output format and Unified context output format when taking a diff?  diff -NBur dir1/ dir2/  diff -NBcr dir1/ dir2/  
What is the difference between Copied context output format and Unified context output format while taking diff?
linux;diff
Apparently you've misread the manual.  The -u flag is for unified context, not Unicode and -c is for copied context, not 'Context format':-c  -C NUM  --context[=NUM]              Output NUM (default 3) lines of copied context.-u  -U NUM  --unified[=NUM]              Output NUM (default 3) lines of unified context.The most straightforward way to find out what is the difference, is to try it out:$ cat >1linediff more^D$ cat >2line ffidmore^D$ diff -c 1 2*** 1   2010-12-14 09:08:48.019797000 +0200--- 2   2010-12-14 09:08:56.029797001 +0200****************** 1,3 ****  line! diff  more--- 1,3 ----  line! ffid  more$ diff -u 1 2--- 1   2010-12-14 09:08:48.019797000 +0200+++ 2   2010-12-14 09:08:56.029797001 +0200@@ -1,3 +1,3 @@ line-diff+ffid moreDo you get what's the difference?