Block Comments in a Shell Script

问题:

Is there a simple way to comment out a block of code in a shell script?

回答1:

In bash:

#!/bin/bash
echo before comment
: <<'END'
bla bla
blurfl
END
echo after comment

The ' and ' around the END delimiter are important, otherwise things inside the block like for example $(command) will be parsed and executed.

For an explanation, see this and this question.

回答2:

There is no block comment on shell script.

Using vi (yes, vi) you can easily comment from line n to m

<ESC>
:10,100s/^/#/

(that reads, from line 10 to 100 substitute line start (^) with a # sign.)

and un comment with

<ESC>
:10,100s/^#//

(that reads, from line 10 to 100 substitute line start (^) followed by # with noting //.)

vi is almost universal anywhere where there is /bin/sh.

回答3:

You can use:

if [ 1 -eq 0 ]; then
  echo "The code that you want commented out goes here."
  echo "This echo statement will not be called."
fi

回答4:

The following should work for sh,bash, ksh and zsh.

The blocks of code to be commented can be put inside BEGINCOMMENT and ENDCOMMENT:

[ -z $BASH ] || shopt -s expand_aliases
alias BEGINCOMMENT="if [ ]; then"
alias ENDCOMMENT="fi"

BEGINCOMMENT
  echo "This line appears in a commented block"
  echo "And this one too!"
ENDCOMMENT

echo "This is outside the commented block"

Executing the above code would result in:

This is outside the commented block

---

In order to uncomment the code blocks thus commented, say

alias BEGINCOMMENT="if : ; then"

instead of

alias BEGINCOMMENT="if [ ]; then"

in the example above.

回答5:

if you can dodge the single quotes:

__='
blah blah comment.
'

回答6:

In Vim:

1. go to first line of block you want to comment
2. shift-V (enter visual mode), up down highlight lines in block
3. execute the following on selection :s/^/#/

4. the command will look like this:

     :'<,'>s/^/#
   

5. hit enter

e.g.

shift-V
jjj
:s/^/#
<enter>

回答7:

You could use Vi/Vim's Visual Block mode which is designed for stuff like this:

Ctrl-V  
Highlight first element in rows you want commented  
Shift-i  
#  
esc  

Uncomment would be:

Ctrl-V  
Highlight #'s  
d  
l  

This is vi's interactive way of doing this sort of thing rather than counting or reading line numbers.

Lastly, in Gvim you use ctrl-q to get into Visual Block mode rather than ctrl-v (because that's the shortcut for paste).

回答8:

So much overengineering...

I consider it really a bad practice to write active code for generating passive code.

My solution: most editors have block select mode. Just use it to add # to all lines you want to comment out. What's the big deal...

Notepad example:

To create: Alt - mousedrag down, press #.

To delete: Alt-mousedrag down, shift-right arrow, delete.

回答9:

A variation on the here-doc trick in the accepted answer by sunny256 is to use the Perl keywords for comments. If your comments are actually some sort of documentation, you can then start using the Perl syntax inside the commented block, which allows you to print it out nicely formatted, convert it to a man-page, etc.

As far as the shell is concerned, you only need to replace 'END' with '=cut'.

echo "before comment"
: <<'=cut'
=pod

=head1 NAME
   podtest.sh - Example shell script with embedded POD documentation

etc.

=cut
echo "after comment"

(Found on "Embedding documentation in shell script")

回答10:

Another mode is: If your editor HAS NO BLOCK comment option,

1. Open a second instance of the editor (for example File=>New File...)
2. From THE PREVIOUS file you are working on, select ONLY THE PART YOU WANT COMMENT
3. Copy and paste it in the window of the new temporary file...
4. Open the Edit menu, select REPLACE and input as string to be replaced '\n'
5. input as replace string: '\n#'
6. press the button 'replace ALL'

DONE

it WORKS with ANY editor