Reputation: 12962

Block Comments in a Shell Script

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

Upvotes: 357

Answers (15)

access_granted

Reputation: 1927

This can be done in a shorter syntax in sh, bash and ksh

<< COMMENT

They worked in the cold, so we could be warm,
some died in the evening, some died at dawn.
They breathed in the coal dust, so kids would be fed,
Gone are those miners, all of them dead.


COMMENT

Upvotes: 1

Mohsen Banan

Reputation: 153

Let's combine the best of all of these ideas and suggestions.

alias _CommentBegin_=": <<'_CommentEnd_'"

as has been said, the single quote is very important, in that without them $(commandName) and ${varName} would get evaluated.

You would use it as:

_CommentBegin_
echo "bash code"
or 
none code can be in here
_CommentEnd_

The alias makes the usage more obvious and better looking.

Upvotes: 1

Ari Singh

Reputation: 1306

You can put the code to comment inside a function. A good thing about this is you can "uncomment" by calling the function just after the definition.

Unless you plan to "uncomment" by calling the function, the text inside the function does not have to be syntactically correct.

ignored() {
  echo this is  comment
  echo another line of comment
}

Many GUI editors will allow you to select a block of text, and press "{" to automatically put braces around the selected block of code.

Upvotes: 4

Rusty75

Reputation: 525

In all honesty, why 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.

Upvotes: 5

Ynnub

Reputation: 21

I like a single line open and close:

if [ ]; then ##
    ...
    ...
fi; ##

The '##' helps me easily find the start and end to the block comment. I can stick a number after the '##' if I've got a bunch of them. To turn off the comment, I just stick a '1' in the '[ ]'. I also avoid some issues I've had with single-quotes in the commented block.

Upvotes: 2

Relative0

Reputation: 1797

Use : ' to open and ' to close.

For example:

: '
This is a
very neat comment
in bash
'

This is from Vegas's example found here

Upvotes: 132

mardocheo

Reputation: 11

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

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

DONE

it WORKS with ANY editor

Upvotes: 0

sunny256

Reputation: 9606

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.

Upvotes: 456

mivk

Reputation: 15049

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")

Upvotes: 2

OscarRyz

Reputation: 199363

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.

Upvotes: 110

horta

Reputation: 1130

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).

Upvotes: 5

devnull

Reputation: 123698

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.

Upvotes: 35

vanvliet.eric

Reputation: 401

if you can dodge the single quotes:

__='
blah blah comment.
'

Upvotes: 30

dannyhan12

Reputation: 972

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

Upvotes: 65

stefanB

Reputation: 79930

In Vim:

go to first line of block you want to comment
shift-V (enter visual mode), up down highlight lines in block
execute the following on selection :s/^/#/
the command will look like this:
```
  :'<,'>s/^/#
```
hit enter

e.g.

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

Upvotes: 16

Block Comments in a Shell Script

Answers (15)

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