Commenting out large sections

You can use iffalse:

iffalse
One morning, as Gregor Samsa was waking up from anxious dreams, he discovered
that in his bed he had been changed into a monstrous verminous bug. He lay on
his armour-hard back and saw, as he lifted his head up a little, his brown,
arched abdomen divided up into rigid bow-like sections.
fi

Of course, this has to align with other syntactical TeX structures in you document whereas you can use % much more freely. The good news is that you can introduce your own switch to make this optional:

newififdraft
drafttrue % or draftfalse

ifdraft
<only shown in draft mode>
else 
<only shown in non-draft mode>
fi

The else part is optional and you could use ifdraft ... fi if you don't need it.

The verbatim package provides a comment environment:

documentclass{article}
usepackage{verbatim}
begin{document}
    This text will be displayed
begin{comment}
    This text will not be displayed.
end{comment}
end{document}

The Not So Short Introduction to LaTeX2e mentions this option on page 6 and remarks: "Note that this won’t work inside complex environments, like math for example."

Another option is the comment package, which, like verbatim provides a comment environment, but offers the option to define arbitrary "throw away" environments that can selectively be enabled or disabled:

documentclass{article}
usepackage{comment}

% uncomment to include stuff in standard comment-environment
%includecomment{comment}

% define a mysection env which content is excluded
excludecomment{mysection}

begin{document}
    This text will be displayed
begin{comment}
    This text will only be displayed, if includecomment{comment} was given
end{comment}
begin{mysection}
    This text will only be displayed, if includecomment{mysection} was given
end{mysection}
end{document}

Additionally, the package provides some simple hooks into the defined environments. Instead of includecomment{mysection} one could also use specialcomment{mysection}{<before code>}{<after code>} to enable a comment section:

% typeset stuff in mycomment with gray text
specialcomment{mysection}{begingroupcolor{gray}}{endgroup}

There are other ways to solve this problem than via (La)TeX.

• You can use your editor's capabilities for commenting to comment out large sections. For instance, in Emacs C-c ; comments (or uncomments) the region (see e.g. http://www.gnu.org/software/auctex/manual/auctex/Commenting.html#Commenting for details).
• You can use version control so that you may delete large sections without being afraid to lose them.

Something that is good about either of these solutions is that they are independent of particular LaTeX packages and code.

This answer obviously depents of the frontend one is using, but in the case of using Kile:

---

Commenting multiple lines with Kile

1) Select the lines you wish to comment out

2) Ctrl - D

---

Uncommenting multiple lines with Kile

1) Select the lines you wish uncomment

2) Ctrl - Shift - D

---

These shortcuts can be changed from Settings -> Configure Shortcuts...

I often paste in plain text such as writing guidelines and comment them out. For me the simplest way is to define a command with an argument which produces no output.

newcommand{comm}[1]{}

And to comment out text:

comm{
Text text text
}

In vi or vim you could comment a section (say line 102-345) like this:

[esc] [:]

you are in command mode now! And type:

102,345s/^/%/

it means substitute the beginning of the line (^) with a % sign.

If using TeXNicCenter, you can highlight the text and

Ctrl + Q to comment the text out

Ctrl + W to uncomment it

For the sake of completeness, I will include the shortcuts for the few editors that I know (with the links to their corresponding original answers).

• Texmaker

Ctrl + T to comment

Ctrl + U to uncomment

You can customize them

• WinEdt

Ctrl + Shift + Alt + → to comment

Ctrl + Shift + Alt + ← to uncomment

Yes, that's four keys (!). However, you can install ToggleComment (a macro) to use Ctrl + Q to toggle between comment and uncomment a block of text.

Anything written after end{document} will be ignored by the compiler. I often use this to cut a document short when troubleshooting, by inserting a second end{document} at the appropriate place.

Is there way to comment out a large section without having to manually putting a % in front of each line?

Not probably what you are looking for, but another approach to easily hide sections is work with child files. It is a rather simple process. Assuming commons usual shortcuts of commons editors (i.e, excluding vim/emacs) will be some like that:

1. Select the section to comment
2. Crtl-X (cut)
3. Write %input{filename}
4. Crtl-N (new document)
5. Crtl-V (paste)

6. Crtl-S filename.tex (save the new document).

   Et voilá. Hereafter restore or comment the section again is as simple as remove/add one % before input. Bonus points: (a)The commented part barely can bothers you while working in the main document and (b) prevent you of accidental deletions on the commented parts (that obviously cannot be detected in the pdf).