Patch - Revision history

JaroslavTulach: /* Trying It */ - 2026-01-21 06:24:04

Trying It

←Older revision		Revision as of 06:24, 21 January 2026
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	The '''-p''' argument is very important. Without it [[patch]] command doesn't know how to interpret the header and locate the ''Channel.java'' file. In such case the [[patch]] command switches to interactive mode - which is quite annoying (but it shows how old the [[patch]] command is - it comes from ages when interactions with user were happening in terminal and not a [[GUI]]). Using '''-p''' argument avoids the interactivity.		The '''-p''' argument is very important. Without it [[patch]] command doesn't know how to interpret the header and locate the ''Channel.java'' file. In such case the [[patch]] command switches to interactive mode - which is quite annoying (but it shows how old the [[patch]] command is - it comes from ages when interactions with user were happening in terminal and not a [[GUI]]). Using '''-p''' argument avoids the interactivity.
		+
		+	With '''-p0''' the above patch seeks for ''channels/Channel.java'' file. One can use '''-p1''' to instruct [[patch]] utility to strip one level from the specified directories. Then the utility would be looking for ''Channel.java'' file only. By default use '''-p1''' for diffs generated by [[git]] '''diff''' command.

	=== Pipe It! ===		=== Pipe It! ===

JaroslavTulach at 06:20, 21 January 2026 - 2026-01-21 06:20:44

←Older revision		Revision as of 06:20, 21 January 2026
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	</source>		</source>

-	=== Quiz ===	+	== Quiz ==

	What do you think about the above text?		What do you think about the above text?
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	* I know the '''-R''' argument of the CLI command		* I know the '''-R''' argument of the CLI command
	* I know something more than [[I\|you]]!		* I know something more than [[I\|you]]!
		+
		+
		+	== Answers ==

	=== Reading ===		=== Reading ===

JaroslavTulach: /* Trying It */ - 2026-01-21 06:19:52

Trying It

←Older revision		Revision as of 06:19, 21 January 2026
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	The '''-p''' argument is very important. Without it [[patch]] command doesn't know how to interpret the header and locate the ''Channel.java'' file. In such case the [[patch]] command switches to interactive mode - which is quite annoying (but it shows how old the [[patch]] command is - it comes from ages when interactions with user were happening in terminal and not a [[GUI]]). Using '''-p''' argument avoids the interactivity.		The '''-p''' argument is very important. Without it [[patch]] command doesn't know how to interpret the header and locate the ''Channel.java'' file. In such case the [[patch]] command switches to interactive mode - which is quite annoying (but it shows how old the [[patch]] command is - it comes from ages when interactions with user were happening in terminal and not a [[GUI]]). Using '''-p''' argument avoids the interactivity.
		+
		+	=== Pipe It! ===
		+
		+	The [[patch]] command expects the changes on stdio - hence the '''<''' to send ''my.diff'' file in. That can be useful to ''cherry pick'' any [[git]] commit. Just try:
		+	<source lang="bash">
		+	$ git show 88e601f \| patch -p1
		+	</source>
		+	and the changes from ''88e601f'' commit will be applied just like you'd typed them manually. Simple way to extract changes from [[git]] history without [[git]] knowing anything about it - e.g. without changing the internals of the local [[git]] repository at all.

	=== Embeddable Format ===		=== Embeddable Format ===

JaroslavTulach: /* Applying a PR from Another GitHub Repository */ - 2026-01-21 06:10:20

Applying a PR from Another GitHub Repository

←Older revision		Revision as of 06:10, 21 January 2026
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	=== Applying a PR from Another GitHub Repository ===		=== Applying a PR from Another GitHub Repository ===
		+
		+	A neat trick is to feed [[patch]] directly from GitHub. Did you know each pull request URL can be appended with ''.diff'' or ''.patch'' and then one gets a plain text page in [[patch]] format? As such one can:

	<source lang="bash">		<source lang="bash">
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	</source>		</source>

		+	Get all changes in 14666 PR and pipe the output directly to [[patch]] utility. Don't forget to remove one directory from paths (as by default [[Git]]'s prepends '''a''' and '''b''' to differentiate between original and target file) by applying '''-p1'''.

	== Conclusion ==		== Conclusion ==

	I have been adding (sometimes complicated) diffs as PR comments for many years and just recently I realized that I am not sure people know how to apply them! That's why I decided to write this down. I find the [[patch]] command line utility very useful. I wish its knowledge would spread. Let this little quiz help with that!		I have been adding (sometimes complicated) diffs as PR comments for many years and just recently I realized that I am not sure people know how to apply them! That's why I decided to write this down. I find the [[patch]] command line utility very useful. I wish its knowledge would spread. Let this little quiz help with that!

JaroslavTulach at 05:45, 21 January 2026 - 2026-01-21 05:45:36

←Older revision		Revision as of 05:45, 21 January 2026
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	$ curl -L https://github.com/enso-org/enso/pull/14666.diff \| patch -p1		$ curl -L https://github.com/enso-org/enso/pull/14666.diff \| patch -p1
	</source>		</source>
		+
		+
		+	== Conclusion ==
		+
		+	I have been adding (sometimes complicated) diffs as PR comments for many years and just recently I realized that I am not sure people know how to apply them! That's why I decided to write this down. I find the [[patch]] command line utility very useful. I wish its knowledge would spread. Let this little quiz help with that!

JaroslavTulach: /* Embeddable Format */ - 2026-01-21 05:41:32

Embeddable Format

←Older revision		Revision as of 05:41, 21 January 2026
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	The above [[diff]] format can be easily embedded into an email and sent as a ''part of a message''. E.g. surrounding the [[patch]] with prose sections as completely OK. The [[patch]] command line tool will just ignore everything not having the appropriate '''diff''' header		The above [[diff]] format can be easily embedded into an email and sent as a ''part of a message''. E.g. surrounding the [[patch]] with prose sections as completely OK. The [[patch]] command line tool will just ignore everything not having the appropriate '''diff''' header
		+
		+	=== Applying a PR from Another GitHub Repository ===
		+
		+	<source lang="bash">
		+	$ curl -L https://github.com/enso-org/enso/pull/14666.diff \| patch -p1
		+	</source>

JaroslavTulach: /* Quiz */ - 2026-01-21 05:37:31

Quiz

←Older revision		Revision as of 05:37, 21 January 2026
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	* I know the '''-R''' argument of the CLI command		* I know the '''-R''' argument of the CLI command
	* I know something more than [[I\|you]]!		* I know something more than [[I\|you]]!
		+
		+	=== Reading ===
		+
		+	My colleague Ilya wrote: ''" In most cases, I will just observe the patch without applying it if it is small enough. (it usually is!)"''. In such case the situation is simple. Lines starting with a single '''-''' are the ones being removed and those starting with a single '''+''' are those being added. The header identifies the file that's being modified, but one doesn't really have to parse it - it is clear the above [[patch]] is related to ''Channel.java'' file.
		+
		+	=== Trying It ===
		+
		+	However sometimes just reading isn't enough. Sometimes we need to apply the [[patch]] locally to try how it behaves. Let's quote Ilya one more time: ''"If it is small enough (a few lines), I will repeat it manually, if ... typing everything by hand is not an option, I will apply it with [[git]]."'' [[I]] am not fully sure how to apply a [[patch]] with [[git]], but let's do it with another program (years older than [[git]]) which is (unsuprisingly) named [[patch]].
		+
		+	<source lang="bash">
		+	$ patch -p0 <my.diff
		+	</source>
		+
		+	The '''-p''' argument is very important. Without it [[patch]] command doesn't know how to interpret the header and locate the ''Channel.java'' file. In such case the [[patch]] command switches to interactive mode - which is quite annoying (but it shows how old the [[patch]] command is - it comes from ages when interactions with user were happening in terminal and not a [[GUI]]). Using '''-p''' argument avoids the interactivity.

	=== Embeddable Format ===		=== Embeddable Format ===

	The above [[diff]] format can be easily embedded into an email and sent as a ''part of a message''. E.g. surrounding the [[patch]] with prose sections as completely OK. The [[patch]] command line tool will just ignore everything not having the appropriate '''diff''' header		The above [[diff]] format can be easily embedded into an email and sent as a ''part of a message''. E.g. surrounding the [[patch]] with prose sections as completely OK. The [[patch]] command line tool will just ignore everything not having the appropriate '''diff''' header

JaroslavTulach at 08:02, 20 January 2026 - 2026-01-20 08:02:11

←Older revision		Revision as of 08:02, 20 January 2026
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	* I know the '''-R''' argument of the CLI command		* I know the '''-R''' argument of the CLI command
	* I know something more than [[I\|you]]!		* I know something more than [[I\|you]]!
		+
		+	=== Embeddable Format ===
		+
		+	The above [[diff]] format can be easily embedded into an email and sent as a ''part of a message''. E.g. surrounding the [[patch]] with prose sections as completely OK. The [[patch]] command line tool will just ignore everything not having the appropriate '''diff''' header

JaroslavTulach at 07:59, 20 January 2026 - 2026-01-20 07:59:27

←Older revision		Revision as of 07:59, 20 January 2026
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-	How can a [[~~path~~]] be distributed? When accepting [[API Patch]]es and having proper [[Git]] repository infrastructure one can probably think of a [[patch]] as a pull request. However, there are older and [[I]]'d like to claim still useful ways to deliver patches that work well with [[Git]] and other versioning systems. In fact this ''old [[good]] way'' is still in the heart of these versioning systems. [[I]] am talking about:	+	How can a [[patch]] be distributed? When accepting [[API Patch]]es and having proper [[Git]] repository infrastructure one can probably think of a [[patch]] as a pull request. However, there are older and [[I]]'d like to claim still useful ways to deliver patches that work well with [[Git]] and other versioning systems. In fact this ''old [[good]] way'' is still in the heart of these versioning systems. [[I]] am talking about:

	<source lang="diff">		<source lang="diff">

JaroslavTulach at 07:59, 20 January 2026 - 2026-01-20 07:59:18

←Older revision		Revision as of 07:59, 20 January 2026
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-	~~What's~~ a [[~~patch~~]]~~? How can it~~ be distributed? When accepting [[API Patch]]es one can probably think of a [[patch]] as a pull request. However, there are older and [[I]]'d like to claim still useful ways to deliver patches that work well with [[Git]] and other versioning systems. In fact this ''old [[good]] way'' is still in the heart of these versioning systems. [[I]] am talking about:	+	How can a [[path]] be distributed? When accepting [[API Patch]]es and having proper [[Git]] repository infrastructure one can probably think of a [[patch]] as a pull request. However, there are older and [[I]]'d like to claim still useful ways to deliver patches that work well with [[Git]] and other versioning systems. In fact this ''old [[good]] way'' is still in the heart of these versioning systems. [[I]] am talking about:

	<source lang="diff">		<source lang="diff">