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243 lines
7.9 KiB
243 lines
7.9 KiB
git-range-diff(1) |
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================= |
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NAME |
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---- |
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git-range-diff - Compare two commit ranges (e.g. two versions of a branch) |
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SYNOPSIS |
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-------- |
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[verse] |
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'git range-diff' [--color=[<when>]] [--no-color] [<diff-options>] |
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[--no-dual-color] [--creation-factor=<factor>] |
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( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> ) |
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DESCRIPTION |
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----------- |
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This command shows the differences between two versions of a patch |
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series, or more generally, two commit ranges (ignoring merge commits). |
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To that end, it first finds pairs of commits from both commit ranges |
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that correspond with each other. Two commits are said to correspond when |
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the diff between their patches (i.e. the author information, the commit |
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message and the commit diff) is reasonably small compared to the |
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patches' size. See ``Algorithm`` below for details. |
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Finally, the list of matching commits is shown in the order of the |
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second commit range, with unmatched commits being inserted just after |
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all of their ancestors have been shown. |
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OPTIONS |
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------- |
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--no-dual-color:: |
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When the commit diffs differ, `git range-diff` recreates the |
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original diffs' coloring, and adds outer -/+ diff markers with |
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the *background* being red/green to make it easier to see e.g. |
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when there was a change in what exact lines were added. This is |
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known to `range-diff` as "dual coloring". Use `--no-dual-color` |
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to revert to color all lines according to the outer diff markers |
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(and completely ignore the inner diff when it comes to color). |
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--creation-factor=<percent>:: |
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Set the creation/deletion cost fudge factor to `<percent>`. |
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Defaults to 60. Try a larger value if `git range-diff` erroneously |
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considers a large change a total rewrite (deletion of one commit |
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and addition of another), and a smaller one in the reverse case. |
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See the ``Algorithm`` section below for an explanation why this is |
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needed. |
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<range1> <range2>:: |
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Compare the commits specified by the two ranges, where |
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`<range1>` is considered an older version of `<range2>`. |
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<rev1>...<rev2>:: |
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Equivalent to passing `<rev2>..<rev1>` and `<rev1>..<rev2>`. |
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<base> <rev1> <rev2>:: |
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Equivalent to passing `<base>..<rev1>` and `<base>..<rev2>`. |
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Note that `<base>` does not need to be the exact branch point |
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of the branches. Example: after rebasing a branch `my-topic`, |
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`git range-diff my-topic@{u} my-topic@{1} my-topic` would |
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show the differences introduced by the rebase. |
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`git range-diff` also accepts the regular diff options (see |
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linkgit:git-diff[1]), most notably the `--color=[<when>]` and |
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`--no-color` options. These options are used when generating the "diff |
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between patches", i.e. to compare the author, commit message and diff of |
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corresponding old/new commits. There is currently no means to tweak the |
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diff options passed to `git log` when generating those patches. |
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CONFIGURATION |
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------------- |
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This command uses the `diff.color.*` and `pager.range-diff` settings |
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(the latter is on by default). |
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See linkgit:git-config[1]. |
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EXAMPLES |
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-------- |
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When a rebase required merge conflicts to be resolved, compare the changes |
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introduced by the rebase directly afterwards using: |
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------------ |
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$ git range-diff @{u} @{1} @ |
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------------ |
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A typical output of `git range-diff` would look like this: |
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------------ |
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-: ------- > 1: 0ddba11 Prepare for the inevitable! |
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1: c0debee = 2: cab005e Add a helpful message at the start |
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2: f00dbal ! 3: decafe1 Describe a bug |
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@@ -1,3 +1,3 @@ |
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Author: A U Thor <author@example.com> |
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-TODO: Describe a bug |
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+Describe a bug |
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@@ -324,5 +324,6 |
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This is expected. |
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-+What is unexpected is that it will also crash. |
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++Unexpectedly, it also crashes. This is a bug, and the jury is |
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++still out there how to fix it best. See ticket #314 for details. |
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Contact |
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3: bedead < -: ------- TO-UNDO |
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------------ |
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In this example, there are 3 old and 3 new commits, where the developer |
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removed the 3rd, added a new one before the first two, and modified the |
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commit message of the 2nd commit as well its diff. |
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When the output goes to a terminal, it is color-coded by default, just |
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like regular `git diff`'s output. In addition, the first line (adding a |
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commit) is green, the last line (deleting a commit) is red, the second |
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line (with a perfect match) is yellow like the commit header of `git |
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show`'s output, and the third line colors the old commit red, the new |
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one green and the rest like `git show`'s commit header. |
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A naive color-coded diff of diffs is actually a bit hard to read, |
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though, as it colors the entire lines red or green. The line that added |
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"What is unexpected" in the old commit, for example, is completely red, |
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even if the intent of the old commit was to add something. |
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To help with that, `range` uses the `--dual-color` mode by default. In |
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this mode, the diff of diffs will retain the original diff colors, and |
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prefix the lines with -/+ markers that have their *background* red or |
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green, to make it more obvious that they describe how the diff itself |
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changed. |
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Algorithm |
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--------- |
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The general idea is this: we generate a cost matrix between the commits |
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in both commit ranges, then solve the least-cost assignment. |
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The cost matrix is populated thusly: for each pair of commits, both |
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diffs are generated and the "diff of diffs" is generated, with 3 context |
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lines, then the number of lines in that diff is used as cost. |
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To avoid false positives (e.g. when a patch has been removed, and an |
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unrelated patch has been added between two iterations of the same patch |
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series), the cost matrix is extended to allow for that, by adding |
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fixed-cost entries for wholesale deletes/adds. |
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Example: Let commits `1--2` be the first iteration of a patch series and |
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`A--C` the second iteration. Let's assume that `A` is a cherry-pick of |
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`2,` and `C` is a cherry-pick of `1` but with a small modification (say, |
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a fixed typo). Visualize the commits as a bipartite graph: |
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------------ |
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1 A |
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2 B |
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C |
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------------ |
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We are looking for a "best" explanation of the new series in terms of |
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the old one. We can represent an "explanation" as an edge in the graph: |
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------------ |
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1 A |
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/ |
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2 --------' B |
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C |
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------------ |
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This explanation comes for "free" because there was no change. Similarly |
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`C` could be explained using `1`, but that comes at some cost c>0 |
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because of the modification: |
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------------ |
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1 ----. A |
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2 ----+---' B |
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`----- C |
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c>0 |
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------------ |
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In mathematical terms, what we are looking for is some sort of a minimum |
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cost bipartite matching; `1` is matched to `C` at some cost, etc. The |
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underlying graph is in fact a complete bipartite graph; the cost we |
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associate with every edge is the size of the diff between the two |
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commits' patches. To explain also new commits, we introduce dummy nodes |
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on both sides: |
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------------ |
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1 ----. A |
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2 ----+---' B |
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o `----- C |
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c>0 |
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o o |
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o o |
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------------ |
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The cost of an edge `o--C` is the size of `C`'s diff, modified by a |
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fudge factor that should be smaller than 100%. The cost of an edge |
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`o--o` is free. The fudge factor is necessary because even if `1` and |
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`C` have nothing in common, they may still share a few empty lines and |
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such, possibly making the assignment `1--C`, `o--o` slightly cheaper |
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than `1--o`, `o--C` even if `1` and `C` have nothing in common. With the |
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fudge factor we require a much larger common part to consider patches as |
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corresponding. |
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The overall time needed to compute this algorithm is the time needed to |
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compute n+m commit diffs and then n*m diffs of patches, plus the time |
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needed to compute the least-cost assigment between n and m diffs. Git |
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uses an implementation of the Jonker-Volgenant algorithm to solve the |
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assignment problem, which has cubic runtime complexity. The matching |
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found in this case will look like this: |
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------------ |
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1 ----. A |
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2 ----+---' B |
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.--+-----' |
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o -' `----- C |
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c>0 |
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o ---------- o |
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o ---------- o |
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------------ |
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SEE ALSO |
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-------- |
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linkgit:git-log[1] |
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GIT |
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--- |
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Part of the linkgit:git[1] suite
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