最近在向 PostgreSQL 社区提交 patch 时，发现其维护者很快就定位到了代码何时由谁更改了，作为一个萌新，我也不好意思问:(，只能自己下来查找资料，经过一番搜索，发现了 git blame 这个命令。
git blame
Git 的 blame 子命令可以显示一个文件每一行最后的修改作者及信息。由此，我们便可以快速定位代码的修改。
例如，我们可以通过如下命令来查看文件的更改。
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| $ git blame ./src/backend/utils/adt/timestamp.c
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 1) /*-------------------------------------------------------------------------
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 2) *
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 3) * timestamp.c
cc26ea9fe2e (Peter Eisentraut 2013-04-20 11:04:41 -0400 4) * Functions for the built-in SQL types "timestamp" and "interval".
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 5) *
97c39498e5c (Bruce Momjian 2019-01-02 12:44:25 -0500 6) * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 7) * Portions Copyright (c) 1994, Regents of the University of California
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 8) *
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 9) *
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 10) * IDENTIFICATION
9f2e2113869 (Magnus Hagander 2010-09-20 22:08:53 +0200 11) * src/backend/utils/adt/timestamp.c
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 12) *
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 13) *-------------------------------------------------------------------------
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 14) */
18952f67446 (Tom Lane 2000-05-29 01:59:17 +0000 15)
18952f67446 (Tom Lane 2000-05-29 01:59:17 +0000 16) #include "postgres.h"
18952f67446 (Tom Lane 2000-05-29 01:59:17 +0000 17)
4bc578eb838 (Marc G. Fournier 1997-04-03 19:58:11 +0000 18) #include <ctype.h>
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 19) #include <math.h>
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 20) #include <limits.h>
dd4eea257b7 (Neil Conway 2005-06-30 03:48:58 +0000 21) #include <sys/time.h>
...
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是不是觉得太长了不方便查看，没关系，git blame 还提供了参数可以控制文件中查看的内容。例如查看文件第 20 行到 40 行之间的改动。
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| $ git blame -L 20,40 ./src/backend/utils/adt/timestamp.c
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 20) #include <limits.h>
dd4eea257b7 (Neil Conway 2005-06-30 03:48:58 +0000 21) #include <sys/time.h>
cb292206c5c (Peter Eisentraut 2000-07-12 22:59:15 +0000 22)
18952f67446 (Tom Lane 2000-05-29 01:59:17 +0000 23) #include "access/xact.h"
5cabcfccce4 (Tom Lane 2002-08-26 17:54:02 +0000 24) #include "catalog/pg_type.h"
df1a699e5ba (Tom Lane 2017-04-05 23:51:27 -0400 25) #include "common/int128.h"
b6d15590f72 (Tom Lane 2008-05-04 23:19:24 +0000 26) #include "funcapi.h"
30f609484d0 (Tom Lane 2003-05-12 23:08:52 +0000 27) #include "libpq/pqformat.h"
8507ddb9c63 (Thomas G. Lockhart 1997-07-01 00:22:46 +0000 28) #include "miscadmin.h"
b8a18ad4850 (Noah Misch 2015-03-01 13:22:34 -0500 29) #include "nodes/makefuncs.h"
c13897983a0 (Robert Haas 2012-02-08 09:33:02 -0500 30) #include "nodes/nodeFuncs.h"
1fb57af9206 (Tom Lane 2019-02-09 18:08:48 -0500 31) #include "nodes/supportnodes.h"
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 32) #include "parser/scansup.h"
bec98a31c55 (Tom Lane 2000-07-17 03:05:41 +0000 33) #include "utils/array.h"
94094c05697 (Marc G. Fournier 1997-03-14 05:58:13 +0000 34) #include "utils/builtins.h"
b5f7cff84f5 (Tom Lane 2005-06-29 22:51:57 +0000 35) #include "utils/datetime.h"
6bf0bc842bd (Tomas Vondra 2018-07-29 03:30:48 +0200 36) #include "utils/float.h"
b5f7cff84f5 (Tom Lane 2005-06-29 22:51:57 +0000 37)
e303a2dbe8c (Tom Lane 2002-09-21 19:52:41 +0000 38) /*
e303a2dbe8c (Tom Lane 2002-09-21 19:52:41 +0000 39) * gcc's -ffast-math switch breaks routines that expect exact results from
a536b2dd80f (Bruce Momjian 2005-07-21 03:56:25 +0000 40) * expressions like timeval / SECS_PER_HOUR, where timeval is double.
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我们还可以通过指定偏移的方式来显示。例如，下面的命令可以到达和上面的命令相同的效果。
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| $ git blame -L 20,+21 ./src/backend/utils/adt/timestamp.c
$ git blame -L 40,-21 ./src/backend/utils/adt/timestamp.c
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如果我们向查看一个函数的变更呢？是否需要先在源文件中查看函数的起止行，然后在指定行号呢？答案当然是 NO。我们可以通过指定函数名来完成这一需求。例如，我想要查看 timestamp_part 函数的更改。
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| $ git blame -L :timestamp_part ./src/backend/utils/adt/timestamp.c
ae526b40703 (Tom Lane 2000-06-09 01:11:16 +0000 4522) timestamp_part(PG_FUNCTION_ARGS)
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 4523) {
220db7ccd8c (Tom Lane 2008-03-25 22:42:46 +0000 4524) text *units = PG_GETARG_TEXT_PP(0);
1dc34982511 (Bruce Momjian 2005-10-15 02:49:52 +0000 4525) Timestamp timestamp = PG_GETARG_TIMESTAMP(1);
ae526b40703 (Tom Lane 2000-06-09 01:11:16 +0000 4526) float8 result;
a70e13a39ec (Tom Lane 2016-03-16 19:09:04 -0400 4527) Timestamp epoch;
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 4528) int type,
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 4529) val;
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4530) char *lowunits;
547df0cc853 (Thomas G. Lockhart 2002-04-21 19:52:18 +0000 4531) fsec_t fsec;
b6b71b85bc4 (Bruce Momjian 2004-08-29 05:07:03 +0000 4532) struct pg_tm tt,
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 4533) *tm = &tt;
41f1f5b76ad (Thomas G. Lockhart 2000-02-16 17:26:26 +0000 4534)
220db7ccd8c (Tom Lane 2008-03-25 22:42:46 +0000 4535) lowunits = downcase_truncate_identifier(VARDATA_ANY(units),
220db7ccd8c (Tom Lane 2008-03-25 22:42:46 +0000 4536) VARSIZE_ANY_EXHDR(units),
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4537) false);
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4538)
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4539) type = DecodeUnits(0, lowunits, &val);
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4540) if (type == UNKNOWN_FIELD)
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4541) type = DecodeSpecial(0, lowunits, &val);
0bd61548ab8 (Tom Lane 2004-05-07 00:24:59 +0000 4542)
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4543) if (TIMESTAMP_NOT_FINITE(timestamp))
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4544) {
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4545) result = NonFiniteTimestampTzPart(type, val, lowunits,
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4546) TIMESTAMP_IS_NOBEGIN(timestamp),
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4547) false);
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4548) if (result)
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4549) PG_RETURN_FLOAT8(result);
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4550) else
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4551) PG_RETURN_NULL();
647d87c56ab (Tom Lane 2016-01-21 22:26:20 -0500 4552) }
...
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您以为这就完了么？Too yong too simple. git blame 的 -L 参数还支持正则表达式。我们可以是下面的正则表达式方式实现上面的需求。
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| $ git blame -L '/^timestamp_part(/,/^}$/' ./src/backend/utils/adt/timestamp.c
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暂时先整理到此处，更多的用法可以查看文档或帮助手册 (man git-blame)。
参考
[1] https://git-scm.com/docs/git-blame