ilugc-talk-ed-16-06-2020

2020-06-16 16:00:17	mohan43u-we	welcome to ILUGC #irc channel
2020-06-16 16:01:14	mohan43u-we	wait for another 5 more mins for people to join
2020-06-16 16:01:46	mohan43u-we	I hope everyone can see the presenter terminal
2020-06-16 16:03:09	-->	mohan43u-kiwi (~mohan43u-@2a01:4f9:c010:82aa::1) has joined #ilugc
2020-06-16 16:03:43	stof9-9	link please
2020-06-16 16:04:00	mohan43u-we	stof9-9: https://training.ilugc.in
2020-06-16 16:04:09	stof9-9	thanks
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2020-06-16 16:04:57	mohan43u-we	lets start the talk
2020-06-16 16:05:23	mohan43u-we	this talk is about 'ed' the text editor
2020-06-16 16:05:51	mohan43u-we	it is created by Ken thomson for original unix
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2020-06-16 16:06:27	mohan43u-we	the idea about ed came when he was in berkeley
2020-06-16 16:06:58	mohan43u-we	he first implemented ed for CTSS then ported it to multics
2020-06-16 16:07:36	mohan43u-we	again, when he developed unix, 'ed' was the editor of choice
2020-06-16 16:07:49	mohan43u-we	along with shell 'sh'
2020-06-16 16:08:38	mohan43u-we	Ken implemented regular expressions in ed way back before unix, in CTSS
2020-06-16 16:08:56	mohan43u-we	ed is a line editor
2020-06-16 16:09:36	mohan43u-we	most of you might be familier with 'vi' which is also a line editor
2020-06-16 16:09:44	mohan43u-we	ed operates in two modes
2020-06-16 16:09:50	mohan43u-we	one is command mode
2020-06-16 16:09:58	mohan43u-we	and the next is input mode
2020-06-16 16:10:13	mohan43u-we	when 'ed' starts, it will be started in command mode
2020-06-16 16:10:32	mohan43u-we	you can switch between command/input modes
2020-06-16 16:11:03	mohan43u-we	before I start the demo, I would like everyone to use the practice terminal to see how ed works
2020-06-16 16:11:14	mohan43u-we	'ed' command is available in practice session
2020-06-16 16:11:26	mohan43u-we	so, lets start now
2020-06-16 16:11:56	mohan43u-we	a simple ed command with show nothing, not even a prompt
2020-06-16 16:12:08	mohan43u-we	just assume that you are in command mode
2020-06-16 16:12:22	mohan43u-we	any characters you type are commands to ed
2020-06-16 16:12:38	mohan43u-we	I just typed ww and press enter
2020-06-16 16:12:55	mohan43u-we	ed said what? what do you mean by 'ww'? I dont understand
2020-06-16 16:13:26	mohan43u-we	ofcourse it didn't say those. but we just assume whenever ed shows '?', it means 'ed' is confused
2020-06-16 16:14:02	mohan43u-we	all those inputs 'ed' dont understand
2020-06-16 16:14:57	mohan43u-we	the only brief help message 'ed' can show is oneliners  when typing 'h' after 'ed' shows '?'
2020-06-16 16:15:34	mohan43u-we	thus, when 'ed' shows ?, we have to type h to get somewhat brief help
2020-06-16 16:15:46	mohan43u-we	now, we are in command mode
2020-06-16 16:15:57	mohan43u-we	and also, there is something called current line
2020-06-16 16:16:42	mohan43u-we	see, the '.' command usually will tell you which line you are, but our buffer is not having any lines
2020-06-16 16:16:53	mohan43u-we	so ed throwed one error
2020-06-16 16:17:17	mohan43u-we	I asked a brief error, and it showed that there is no address as current line
2020-06-16 16:17:27	mohan43u-we	now, add some content to our current buffer
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2020-06-16 16:18:01	mohan43u-we	the input 'i', 'a', 'A' can help switch 'ed' from command mode to input mode
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2020-06-16 16:18:58	mohan43u-we	so I added three lines, now I want to switch back to command mode,
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2020-06-16 16:21:37	mohan43u-we	any line start with '.' character in input mode will switch 'ed' to command mode
2020-06-16 16:21:37	mohan43u-we	now, ed is in command mode
2020-06-16 16:21:37	mohan43u-we	see, when I typed a line forgetting that I'm in command mode, 'ed' throwed error
2020-06-16 16:21:37	mohan43u-we	just to get a brief help
2020-06-16 16:21:37	mohan43u-we	now, we can see how to print the buffer
2020-06-16 16:21:38	mohan43u-we	in ed, every line have a address associated with it
2020-06-16 16:21:38	mohan43u-we	line address start from 1
2020-06-16 16:22:01	Guest67250	hi
2020-06-16 16:22:14	mohan43u-we	I just typed '1' and pressed enter, 'ed' showed that line
2020-06-16 16:22:37	mohan43u-we	'1' internally befomes '1p'
2020-06-16 16:22:50	mohan43u-we	here 'p' means 'print'
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2020-06-16 16:23:54	mohan43u-we	most of the ed command have this general syntex <start>,<end><command>
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2020-06-16 16:24:30	mohan43u-we	I just typed 1,$p
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2020-06-16 16:24:40	mohan43u-we	here, $ represents the end line
2020-06-16 16:24:46	mohan43u-we	or the last line
2020-06-16 16:25:13	mohan43u-we	the same, line 1,$p, but instead of using p, I used n
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2020-06-16 16:25:24	mohan43u-we	n means print along with line addresses
2020-06-16 16:26:00	mohan43u-we	now, remember I said about '.'?
2020-06-16 16:26:03	mohan43u-we	now try that
2020-06-16 16:26:26	mohan43u-we	see, the '.' represents line which was last modified
2020-06-16 16:26:55	mohan43u-we	the third line was the line we added last, so '.' now points to the third line
2020-06-16 16:27:49	mohan43u-we	if you dont give any address but simply try to use the command, then it means, you are operating on the current line which is the third line
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2020-06-16 16:28:36	mohan43u-we	the current line now changed to first line after I typed 1, because it is the line last printed (a command operated on it)
2020-06-16 16:28:42	--	Mir is now known as Guest91114
2020-06-16 16:29:40	mohan43u-we	as you see, by typing ',n' or ',p' we are implicitly telling '1,$n' or '1,$p'
2020-06-16 16:30:11	mohan43u-we	now, we have a buffer with three lines in 'ed'
2020-06-16 16:30:30	mohan43u-we	this buffer is still in memory, not written to file in filesystem
2020-06-16 16:31:01	mohan43u-we	the command to write the buffer back to file system is 'w'
2020-06-16 16:31:28	mohan43u-we	we need to give 'w' a filename, otherwise 'ed' with throw its confused signal
2020-06-16 16:31:40	mohan43u-we	see, it says no current filename
2020-06-16 16:32:16	mohan43u-we	after I gave filename, it showed how many characters it got written into the file
2020-06-16 16:33:03	mohan43u-we	I did a mistake in the fourth line
2020-06-16 16:33:20	mohan43u-we	I want to delete it, so here is how we delete
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2020-06-16 16:33:34	mohan43u-we	the fourth line gone
2020-06-16 16:34:38	mohan43u-we	see, I mistakenly typed ',n' when I was in input mode, quickly realized that I was in input mode
2020-06-16 16:34:56	mohan43u-we	so I switched back to command mode using '.' in a single line and then typed only 'd'
2020-06-16 16:35:15	mohan43u-we	which means, delete the last operated line (or simply the current line)
2020-06-16 16:35:31	mohan43u-we	now we have 4 lines
2020-06-16 16:36:01	stof999-kiwi	:)
2020-06-16 16:36:19	mohan43u-we	but if you look at the file which we wrote, we only have three lines
2020-06-16 16:36:29	mohan43u-we	it means, the fourth line was not written
2020-06-16 16:36:39	mohan43u-we	written into the filesystem
2020-06-16 16:36:55	mohan43u-we	we have to write everytime we modify the buffer
2020-06-16 16:37:25	stof999-kiwi	?
2020-06-16 16:37:30	mohan43u-we	emacs can save all your updates into the buffer in a temporary file which starts with '#<filename>#',
2020-06-16 16:37:42	mohan43u-we	same way, vi can store your current buffer as .swp file
2020-06-16 16:38:04	mohan43u-we	but 'ed' is a dumb one, it will not do unless you ask it to do
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2020-06-16 16:38:12	mohan43u-we	stof999-kiwi: please ask
2020-06-16 16:38:25	stof999-kiwi	no warning? nothing?
2020-06-16 16:38:32	mohan43u-we	stof999-kiwi: nothing
2020-06-16 16:38:53	mohan43u-we	stof999-kiwi: thats why it is called real programmers editor :)
2020-06-16 16:39:11	mohan43u-we	continuing my talk.
2020-06-16 16:39:31	mohan43u-we	here is how we can update the content of the current buffer into the filesystem
2020-06-16 16:39:51	mohan43u-we	see, last time when we did 'w', 'ed' throwed confused signal, butnow
2020-06-16 16:39:56	mohan43u-we	but now, it didn't
2020-06-16 16:40:27	mohan43u-we	because we already told 'ed' that associate 'ed-turorial.txt' file with the current buffer
2020-06-16 16:40:53	mohan43u-we	or in other ways, the filename we gave to 'ed' was used as current file for the current buffer
2020-06-16 16:41:29	mohan43u-we	now you can see that both buffer contents and file contents matches
2020-06-16 16:41:53	mohan43u-we	to quit 'ed', just type q
2020-06-16 16:42:46	mohan43u-we	see, I just typed one more line (added content to buffer), but that line was not saved into filesystem
2020-06-16 16:43:07	mohan43u-we	'ed' just throwed its famous confused signal
2020-06-16 16:43:11	mohan43u-we	let see what it says
2020-06-16 16:43:33	mohan43u-we	it says buffer was modified but it is not updated into filesystem
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2020-06-16 16:43:54	mohan43u-we	now I wrote the buffer content back to filesystem
2020-06-16 16:44:13	mohan43u-we	now 'q' didn't throw any error and simply edited
2020-06-16 16:44:56	mohan43u-we	so this file 'ed-tutorial.txt' is the final product of our 'ed' session
2020-06-16 16:45:14	mohan43u-we	before moving to the next part, if anyone have query please raise
2020-06-16 16:46:11	mohan43u-we	continuing my talk
2020-06-16 16:47:44	mohan43u-we	I just started 'ed' and loaded the current buffer with the content from 'ed-tutorial.txt' file
2020-06-16 16:47:52	mohan43u-we	with the 'e' command
2020-06-16 16:48:27	mohan43u-we	'e' command will read the contents from the file and load the current buffer with the contents
2020-06-16 16:49:32	mohan43u-we	without quiting ed, I again typed 'e' command to load another file
2020-06-16 16:50:09	mohan43u-we	so 'e' command flushed the current buffer, and loaded the new file
2020-06-16 16:50:46	mohan43u-we	I forgot the filename which we used, so I run a shell command from inside 'ed' using '!'
2020-06-16 16:51:32	mohan43u-we	now I loaded the correct file
2020-06-16 16:53:21	mohan43u-we	the 'c' command will change the line you specify
2020-06-16 16:54:01	mohan43u-we	more specifically, it will switch 'ed' into input mode after flush out that specific line
2020-06-16 16:54:08	mohan43u-we	lets change the first line
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2020-06-16 16:55:26	mohan43u-we	instead of giving line address, you can provide basic regular expressions to ed commands
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2020-06-16 16:55:55	mohan43u-we	'/third/'n means, print any line which contains word 'third'
2020-06-16 16:57:36	mohan43u-we	when we omit 'g' at the beginning, /<re>/n will not into the lines from the current line to the end line and look for the <re>
2020-06-16 16:57:50	mohan43u-we	currently we are in the second line
2020-06-16 16:57:59	mohan43u-we	now search for buffer
2020-06-16 16:58:22	mohan43u-we	it only printed the next line which contains word 'buffer'
2020-06-16 16:58:39	mohan43u-we	now, we are currently in third line
2020-06-16 16:59:14	mohan43u-we	?<re>? syntex will search for <re> from current line back to first line
2020-06-16 16:59:43	mohan43u-we	just showing example how '?' works
2020-06-16 17:00:54	mohan43u-we	so the ?<re>? wrap around and search backwards
2020-06-16 17:01:24	mohan43u-we	/<re>/ wraps and search forward
2020-06-16 17:02:03	mohan43u-we	the global 'g' command operates on the whole buffer matching any line which contains 'buffer'
2020-06-16 17:02:30	mohan43u-we	g/<re>/p
2020-06-16 17:02:50	mohan43u-we	is basically the famous 'grep' command
2020-06-16 17:04:13	mohan43u-we	'ed' operates with BRE
2020-06-16 17:04:19	mohan43u-we	basic regular expression
2020-06-16 17:04:40	shrini1	Wow
2020-06-16 17:05:11	mohan43u-we	I thought of giving brief intro to BRE, but the talk time is not enough to explain about BRE
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2020-06-16 17:06:18	mohan43u-we	https://man7.org/linux/man-pages/man7/regex.7.html
2020-06-16 17:06:29	mohan43u-we	this is a simple intro to Regular Expressions
2020-06-16 17:06:56	mohan43u-we	this is proper man page of 'ed' https://man7.org/linux/man-pages/man1/ed.1p.html
2020-06-16 17:07:33	mohan43u-we	'ed' is part of posix, so any operating system which claims to be posix compatible will have 'ed'
2020-06-16 17:08:09	mohan43u-we	the link to the manual page which I gave will provide details about how 'ed' should operate in a posix environment
2020-06-16 17:08:39	mohan43u-we	different unix flavours implemented 'ed' in various ways
2020-06-16 17:09:16	mohan43u-we	most of the Linux distros uses GNU 'ed'
2020-06-16 17:09:30	mohan43u-we	https://www.gnu.org/software/ed/
2020-06-16 17:09:55	stof999-kiwi	?
2020-06-16 17:10:33	mohan43u-we	concluding my talk with this famous joke about editors https://xkcd.com/378/
2020-06-16 17:11:05	mohan43u-we	thats it. thanks for attendint the talk. please ask questions/discuss freely
2020-06-16 17:11:10	mohan43u-we	stof999-kiwi: please ask
2020-06-16 17:11:18	stof999-kiwi	clap, clap
2020-06-16 17:11:20	mohan43u-we	^s/attendint/attending/g
2020-06-16 17:11:53	mohan43u-we	stof999-kiwi: thanks
2020-06-16 17:12:33	stof999-kiwi	what are the main diff between posix- and gnu-ed?
2020-06-16 17:13:17	mohan43u-we	stof999-kiwi: gnu contains few more then the posix
2020-06-16 17:14:02	mohan43u-we	stof999-kiwi: I'm not aware of the differences right now. I need to check the differences
2020-06-16 17:14:37	stof999-kiwi	it's ok. thanks
2020-06-16 17:16:20	mohan43u-we	talk concluded. #ilugc channel floor is open to anyone to talk. feel free to hang in hear and have fun
2020-06-16 17:16:33	mohan43u-we	s/^hear/here/g