Viewing the evolution of a line or function

git log's -L flag allows us to trace the evolution of a single line, a range of lines, or a function.

Line range

To view the history of a range of lines, specify <start>:<end> following -L:

git log -L5,15:pom.xml

To view a single line, use the same line number for both <start> and <end>:

git log -L9,9:pom.xml

Function

To view the history of a function, specify :<funcname> following -L, where <funcname> is a regular expression.

git log -L:getUserById:path/to/my/Class.java

From the git-log manpage:

The function names are determined in the same way as git diff works out patch hunk headers

This is, by default:

... a line that begins with an alphabet, an underscore or a dollar sign

This won't be approriate in many cases, particularly not in Java where methods are members of classes, meaning they are indented. The default funcname regex does not match any lines with leading whitespace. To change how hunk headers are determined, we need to update .gitattributes within the project:

*.java  diff=java

We can define a custom regular expression that suits our purposes, but there are a few built-in patterns to make this easier, and java is one of them, so we're all set.

Source:

• LESS='-p Defining a custom hunk-header' man gitattributes

• LESS='-p -L<start>' man git-log