Comments on: Get sed savvy – part 2

By: Get sed savvy - part 3

Get sed savvy - part 3 — Thu, 07 Aug 2008 23:06:34 +0000

[...] Soon we’ll be looking at awk and other tools to continue the quest for command-line fluency. If you haven’t already, install Cygwin and check out part 1 and part 2. [...]

By: Eric Wendelin

Eric Wendelin — Tue, 29 Jul 2008 18:44:13 +0000

@Chris:
You beat me to mentioning it :). A very cool tidbit about sed, there.

By: Chris

Chris — Mon, 28 Jul 2008 23:37:42 +0000

I know there are a million things worth mentioning about sed, but an often overlooked one is that the regular expression separators can be any character as long as they are consistent. The following examples all perform the same inline global search for “/tmp” and replace it with “/home” in the test.txt file:

sed -i ’s/\/tmp/\/home/g’ test.txt # ugly and requires escaping

sed -i ’s|/tmp|/home|g’ test.txt # better but still cluttered

sed -i ’s_/tmp_/home_g’ test.txt # open and easily readable

Changing the regular expression separator can be helpful at maintaining readability, especially when you are matching something with a “/”.

-Chris

By: Eric Wendelin

Eric Wendelin — Fri, 25 Jul 2008 06:14:37 +0000

@Reginald:

Fair request :) Here is one of my references linked in the comments and 1st article: http://www.student.northpark.edu/pemente/sed/sed1line.txt

By: gialloporpora

gialloporpora — Thu, 24 Jul 2008 21:53:12 +0000

Good tutorial :-)
I am a Windows user, but I like sed very much, it is one of the most useful tool that I know (I am using the Gnuwin32 sed).
I have used it to recover “deleted messages in Thunderbird (they are deleted only when folder are compacted, first of compating they are hidden):

http://www.gialloporpora.netsons.org/usare-sed-per-recuperare-le-email-invisibili-in-thunderbird/268/

or to create bookmarklet. I prefere to work with a javascript code in localost with a standard bookmarklet that inject it in my pages, but when I have finished I transform the file.js in a bookmarklet with this sed line (I have found the code in some place on the web, but I don’t remember the URL):

sed -e :a -e “/$/N; s/\n//; ta” > file.js

this is an windows syntax.

Ciao
Sandro

By: Reginald Wadham

Reginald Wadham — Thu, 24 Jul 2008 08:38:01 +0000

Can we have more examples?

By: Eric Wendelin

Eric Wendelin — Wed, 23 Jul 2008 20:15:55 +0000

@David Regal:
Glad I could clear it up. The comma thing is probably the best feature of sed besides substitution.

By: David Regal

David Regal — Wed, 23 Jul 2008 19:43:02 +0000

Finally, the mysterious comma is explained. Sed takes the two matches like addresses, but wow, that’s not documented well in the man pages.

Gracias.

Details:

I was looking at someone else’s sed code that had a comma between two patterns. When I played with it, I was thinking the comma was a commmand, and couldn’t figure it out until I read this page.

When I would take the comma out, or replace it with another character (e.g. a period), sed would complain of a unknown command.

$./script
sed: -e expression #1, char 132: unknown command: `.’
$

Now I understand. Taking away the comma changes the context of the pattern (no longer an address).