POSIX 7 http://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html, implemented on most Linux on the GNU https://www.gnu.org/software/diffutils/ package.
http://en.wikipedia.org/wiki/Diff_utility
Compare the contents of two files and show only where they differ. Can also operate recursively in directories with -r.
Mathematically, each unique line is treated as a different input token, and then (TODO confirm) it computes the http://en.wikipedia.org/wiki/Levenshtein_distance between the two strings.
Equal:
diff <(printf '0\n1\n2\n') <(printf '0\n1\n2\n')
Output: none.
Deletion of one line:
diff <(printf '0\n1\n2\n') <(printf '0\n2\n')
Output:
2d1
< 1
Deletion of one line further down:
diff <(printf '0\n1\n2\n3\n') <(printf '0\n1\n3\n')
Output:
3d2
< 2
Deletion of two lines:
diff <(printf '0\n1\n2\n3\n') <(printf '0\n3\n')
Output:
2,3d1
< 1
< 2
Two deletions:
diff <(printf '0\n1\n2\n3\n4\n5\n6\n') <(printf '0\n2\n3\n4\n6\n')
Output:
2d1
< 1
6d4
< 5
Two double deletions:
diff <(printf '0\n1\n2\n3\n4\n5\n6\n') <(printf '0\n3\n6\n')
Output:
2,3d1
< 1
< 2
5,6d2
< 4
< 5
Addition of one line:
diff <(printf '0\n2\n') <(printf '0\n1\n2\n')
Output:
1a2
> 1
Addition of two lines:
diff <(printf '0\n3\n') <(printf '0\n1\n2\n3\n')
Output:
1a2,3
> 1
> 2
Change one line:
diff <(printf '0\n1\n2\n') <(printf '0\na\n2\n')
Output:
2c2
< 1
---
> a
Change two lines:
diff <(printf '0\n1\n2\n3\n') <(printf '0\na\nb\n3\n')
Output:
2,3c2,3
< 1
< 2
---
> a
> b
Looks like Git's diff (unified format):
diff -u <(printf '0\n1\n2\n') <(printf '0\n2\n')
Output:
--- /dev/fd/63 2015-04-05 00:28:34.975628915 +0200
+++ /dev/fd/62 2015-04-05 00:28:34.979628915 +0200
@@ -1,3 +1,2 @@
0
-1
2
Operate in directories:
mkdir a
touch a/a
touch a/c
mkdir b
touch b/b
touch b/c
diff a b
No simple way: http://stackoverflow.com/questions/8800578/colorize-diff-on-the-command-line
Use git diff.
Unfortunately git diff cannot deal with pipe inputs: