SED question, can't delete first line from a file

JockVSJock · 06-16-2016, 12:07 PM

Have a test file called file_sed.

Code:

Cygwin 
Unix 
Linux
Solaris
AIX

If using Special Character '^' because I want to remove the 1st line.

Code:

sed '^d' file_sed

I get

Code:

sed: -e expression #1, char 1: unknown command: `^'

I can use the Special Character '$' to remove the last line of the file.

Code:

sed '$d' file_sed 

Cygwin 
Unix 
Linux 
Solaris

It works.

I would think the '^' would not show the 1st line like the '$' character doesn't show the last line of the file.

Is my thinking correct?

Mitt Green · 06-16-2016, 12:33 PM

To simply remove the first line, try this:

Code:

sed -i -e "1d" file_sed

keefaz · 06-16-2016, 12:52 PM

$ is not a reg exp in this context, but match last line
man sed

Code:

The following address types are supported:

number      Match only the specified line number (which  increments  cumula-
            tively  across  files,  unless the -s option is specified on the
            command line).

...
$      Match the last line.

JockVSJock · 06-16-2016, 12:53 PM

Quote:

Originally Posted by Mitt Green

To simply remove the first line, try this:

Code:

sed -i -e "1d" file_sed

Well...sure.

However I want to get familiar with SED's special characters, and I'm not understanding the why behind the '^' and the 1st line out of the file. And why it works with '$' with the last line.

thanks

grail · 06-16-2016, 01:26 PM

I would suggest you sit down with the man page and http://www.grymoire.com/Unix/Sed.html, then work your way through that entire web site as it covers all there is to know about sed

JockVSJock · 06-16-2016, 07:02 PM

Quote:

Originally Posted by grail

I would suggest you sit down with the man page and http://www.grymoire.com/Unix/Sed.html, then work your way through that entire web site as it covers all there is to know about sed

Alright, I've booked marked that site. I have a number of them that I'm using to teach myself SED:

http://www.thegeekstuff.com/2009/09/...itute-command/

http://www.theunixschool.com/2013/02...csv-files.html

http://www.theunixschool.com/2012/06...e-line-or.html

http://www.theunixschool.com/2014/08...line-file.html

In the back of my mind, I'm wondering how long it will take to get good at SED. 90 days? 1 year?

ThePenguinRules · 06-16-2016, 08:01 PM

grail · 06-17-2016, 12:00 AM

I agree that it is the old 'how long is a piece of string' type question. I have understanding of the basics and a bit past but generally just use the site I listed when stuck

chrism01 · 06-17-2016, 01:55 AM

I'm definitely a 'one-liner' guy for sed.

If I want anything more complex I break out Perl because I used to do a LOT of work in Perl and I also find the regex docs a bit easier to follow (prob just familiarity I suppose...).
I highly recommend http://regex.info/book.html for all things regex ...

syg00 · 06-17-2016, 02:09 AM

Quote:

Originally Posted by JockVSJock

In the back of my mind, I'm wondering how long it will take to get good at SED. 90 days? 1 year?

Whenever you have these thoughts, translate it thus

Code:

s/SED/CHESS/

Knowing the basic definitions doesn't make one "good".

ThePenguinRules · 06-17-2016, 05:34 PM

ThePenguinRules · 06-17-2016, 09:28 PM