How to search through commit history using either of:

• git log
• git grep

Examples use the Git repository for the “Pro Git” book found here.

The git log command supports looking for commits by the content of their commit messages, or even the content of the diff they introduced. All examples here can be enhanced with the regular git log options.

$ git log --author="Robert P. J. Day"
$ git log --author="Robert P\. J\. Day"
$ git log --author="P\. J\."
$ git log --author="Robert P. J. Day" --oneline
$ git log --author="Robert P. J. Day" --oneline | wc -l
104
$ git log -i --author="robert p. j. day"

--since=<date>, --after=<date>
    Show commits more recent than a specific date.

--until=<date>, --before=<date>
    Show commits older than a specific date.

So:

$ git log --since="Feb 1, 2019"
$ git log --author="Ben Straub" --since="Jan 1, 2019" --until="Feb 1, 2019"

--grep=<pattern>
    Limit the commits output to ones with log message that
    matches the specified pattern (regular expression). With
    more than one --grep=<pattern>, commits whose message
    matches any of the given patterns are chosen (but see
    --all-match).

...

--all-match
    Limit the commits output to ones that match all given
    --grep, instead of ones that match at least one.

--invert-grep
    Limit the commits output to ones with log message that do
    not match the pattern specified with --grep=<pattern>.

Ignoring case:

$ git log --grep="Tagging" --oneline | wc -l
6
$ git log --grep="tagging" --oneline | wc -l
9
$ git log -i --grep="tagging" --oneline | wc -l
13
$

Specifying AND or OR:

$ git log -i --grep="tagging" --grep="rewording" --oneline | wc -l
66
$ git log -i --grep="tagging" --grep="rewording" --all-match --oneline | wc -l
2
$ git log -i --grep="tagging" --grep="rewording" --all-match 
commit 110e27b003c10b4574ee49a47a090e125d6c4811
Merge: 72d6a54 a402fcf
Author: Ben Straub <ben@straub.cc>
Date:   Mon Oct 16 10:30:02 2017 -0700

    Merge pull request #866 from rpjday/tagging
    
    Add TIP to tagging section explaining "-l"; also some rewording

commit a402fcf53fb0d8d0c165ca9ee9ce233ea955cb85
Author: Robert P. J. Day <rpjday@crashcourse.ca>
Date:   Mon Oct 16 01:44:21 2017 -0700

    Add TIP to tagging section explaining "-l"; also some rewording
    
      - Clarify the need for [-l|--llist]
      - Some minor rewording
$

In many cases, merge commits are of no interest since they simply merge commits that produce actual change.

$ git log --author="Ben Straub" --oneline | wc -l
803
$ git log --author="Ben Straub" --oneline --no-merges | wc -l
300
$

Look for specified patterns in the tracked files in the work
tree, blobs registered in the index file, or blobs in given
tree objects. Patterns are lists of one or more search
expressions separated by newline characters. An empty string as
search expression matches all lines.

Options:

[-a | --text] [-I] [--textconv] [-i | --ignore-case] [-w | --word-regexp]
  [-v | --invert-match] [-h|-H] [--full-name]
  [-E | --extended-regexp] [-G | --basic-regexp]
  [-P | --perl-regexp]
  [-F | --fixed-strings] [-n | --line-number] [--column]
  [-l | --files-with-matches] [-L | --files-without-match]
  [(-O | --open-files-in-pager) [<pager>]]
  [-z | --null]
  [ -o | --only-matching ] [-c | --count] [--all-match] [-q | --quiet]
  [--max-depth <depth>] [--[no-]recursive]
  [--color[=<when>] | --no-color]
  [--break] [--heading] [-p | --show-function]
  [-A <post-context>] [-B <pre-context>] [-C <context>]
  [-W | --function-context]
  [--threads <num>]
  [-f <file>] [-e] <pattern>
  [--and|--or|--not|(|)|-e <pattern>...]
  [-recurse-submodules] [--parent-basename <basename>]
  [ [--[no-]exclude-standard] [--cached | --no-index | --untracked] | tree>...]
  [--] [<pathspec>...]

• grep.lineNumber
• grep.patternType
• grep.extendedRegexp
• grep.threads
• grep.fullName
• grep.fallbackToNoIndex

See man git-config.

$ git grep -il torvalds 
book/01-introduction/sections/history.asc
book/07-git-tools/sections/debugging.asc
$