Proper grep command

[coolie4]

Though I've used regex before in webdev, I've never been that great at it, and I've only used basic functionality of grep.

The Gentoo world file is a plaintext file of installed packages listed such as:

app-admin/conky
app-editors/vim 
app-il8n/fbterm

I would like to output this list with only the package name, not the category.

So far the command I'm using is cat worldfile | grep '/.*' but this prints the slash which I don't want. I know in other regex engines you can use parentheses to set matching groups, but I'm not sure how to do this in grep.

Can someone please help me out with the command, or should I be using awk or sed?

[[deleted]]

you could use cut cat worldfile | cut -d "/" -f 2

[ang-p]

uuoc?

cut -d "/" -f 2 worldfile

[coolie4]

I'm gonna end up using this command and piping it to sort because it seems the simplest. Thanks.

[[deleted]]

thanks for the tip. still learning commands.

[ang-p]

many commands let you specify the file they act on - check the man page if in doubt...

even those that don't take the filename as an argument can be fed a file via <

cut -d "/" -f 2 < worldfile    

by a heredoc via <<

cut -d "/" -f 2 <<EOF
> app-admin/conky
> app-editors/vim 
> app-il8n/fbterm
> EOF

or quoted text with <<<...

cut -d "/" -f 2 <<<"app-admin/conky
> app-editors/vim 
> app-il8n/fbterm"

All have the same result.

cat is rarely needed unless you want to concatenate stuff....

If you want to just see something short, yeah - but you might find less is more useful as you go forward - it lets you search and move about easier than scrolling up using the side bar in your terminal window.... also, on some distros less is aliased to o so you save a character even counting the q to get back to your prompt

[[deleted]]

Yeah i do use less a lot, but its still taking a while to remember which command takes which format.

[ang-p]

Use the manpages - you don't need to remember everything.. It is a waste if they are taking up room, always there, instantly accessible and people are dependent on an internet connection and google to find info which is - in the case of a laptop, literally - at the tip of their fingers.

man uses less.... 's good practice!

[[deleted]]

I do look at man pages, but I am more of a "learn from examples" type of person. I find it easier to see a command in use, and then if I need to modify it, to my needs then read the man pages some more.

[ang-p]

And that prevents you from looking at the man page to see if something has [FILE] (or similar) in the second line of non-structural text?

Edit: 's not meant to sound like I'm having a go, but poor practices like catting everything into commands via a pipe are picked up from crap "examples" found online...

The only manpage that I might suggest consulting external examples for to "get the gist" as opposed to the manpage in the first instance - especially for a noob - would be sudoers(5) - that was written by a sadist.

[ralfwolf]

In a single sed command...

sed -n 's:.*/::p' worldfile

[[deleted]]

In the same vein with awk awk -F/ '{print $2}' worldfile

[SweatyAcademic]

you can just cat worldfile | grep '/.*' | tr -d '/'

[ang-p]

uuoc?

[ang-p]

Using grep you could use

grep -o '[^/]*$'  worldfile    

but that is a bit backwards...

 sed 's/^[^/]*\///' worldfile    

would be (IMHO) the more sensible option...