Way to create multiline comments in Bash

Question

I have recently started studying shell script and I d like to be able to comment out a set of lines in a shell script  I mean like it is in case of C Java       comment1    comment2     comment3       How could I do that

User · Accepted Answer

Use     to open and   to close   For example       This is a very neat comment in bash

User · Answer

Here s how I do multiline comments in bash   This mechanism has two advantages that I appreciate   One is that comments can be nested   The other is that blocks can be enabled by simply commenting out the initiating line      bin bash      lt  lt       block A  echo  foo    1 gt  amp 2 fn data1 echo  foo    1 gt  amp 2    lt  lt       block B  fn data2    exit exit 1      block B echo  can t happen  1 gt  amp 2      block A   In the example above the  B  block is commented out  but the parts of the  A  block that are not the  B  block are not commented out   Running that example will produce this output   foo     example  line 5  fn  command not found foo   can t happen

User · Answer

Simple solution  not much smart    Temporarily block a part of a script   if false  then     while you respect syntax a bit  please     do write here  almost  whatever you want      but when you are     done   write fi   A bit sophisticated version   time of debug false   Let s set this variable at the beginning of a script  if  time of debug  then   in a middle of the script       echo I keep this code aside until there is the time of debug  fi

User · Answer

Note  I updated this answer based on comments and other answers  so comments prior to May 22nd 2020 may no longer apply  Also I noticed today that some IDE s like VS Code and PyCharm do not recognize a HEREDOC marker that contains spaces  whereas bash has no problem with it  so I m updating this answer again  Bash does not provide a builtin syntax for multi-line comment but there are hacks using existing bash syntax that  quot happen to work now quot   Personally I think the simplest  ie least noisy  least weird  easiest to type  most explicit  is to use a quoted HEREDOC  but make it obvious what you are doing  and use the same HEREDOC marker everywhere   lt  lt     BLOCK-COMMENT  line 1 line 2  line 3 line 4    BLOCK-COMMENT  Single-quoting the HEREDOC marker avoids some shell parsing side-effects  such as weird subsitutions that would cause crash or output  and even parsing of the marker itself  So the single-quotes give you more freedom on the open-close comment marker  For example the following uses a triple hash which kind of suggests multi-line comment in bash  This would crash the script if the single quotes were absent  Even if you remove      the FOO   would crash the script  or cause bad substitution to be printed if no set -e  if it weren t for the single quotes  set -e   lt  lt     BLOCK-COMMENT  something something   FOO    something more comment    BLOCK-COMMENT  ls  You could of course just use set -e   lt  lt       something something   FOO    something more comment      ls  but the intent of this is definitely less clear to a reader unfamiliar with this trickery  Note my original answer used      BLOCK COMMENT   which is fine if you use vanilla vi vim but today I noticed that PyCharm and VS Code don t recognize the closing marker if it has spaces  Nowadays any good editor allows you to press ctrl-  or similar  to un comment the selection  Everyone definitely understands this    something something   FOO    something   more comment   yet another line of comment  although admittedly  this is not nearly as convenient as the block comment above if you want to re-fill your paragraphs  There are surely other techniques  but there doesn t seem to be a  quot conventional quot  way to do it  It would be nice if     gt  and     lt  could be added to bash to indicate start and end of comment block  seems like it could be pretty straightforward

User · Answer

Multiline comment in bash     lt  lt  END COMMENT  This is a heredoc   lt  lt   redirected to a NOP command      The single quotes around END COMMENT are important  because it disables variable resolving and command resolving within these lines   Without the single-quotes around END COMMENT  the following two        commands would get executed    gibberish command   rm -fr mydir  comment1 comment2  comment3 END COMMENT

User · Answer

what s your opinion on this one   function giveitauniquename       so this is a comment   echo  there s no need to further escape apostrophes etc if you are commenting your code this way    the drawback is it will be stored in memory as a function as long as your script runs unless you explicitly unset it   only valid-ish bash allowed inside for instance these would not work without the  pound  signs    1  for       2  this  wouldn t work either   function giveitadifferentuniquename           echo nestable

User · Answer

I tried the chosen answer  but found when I ran a shell script having it  the whole thing was getting printed to screen  similar to how jupyter notebooks print out everything in    xx    quotes  and there was an error message at end  It wasn t doing anything  but  scary  Then I realised while editing it that single-quotes can span multiple lines  So   lets just assign the block to a variable   x   echo  these lines will all become comments   echo  just make sure you don t use single-quotes    ls -l date

User · Answer

After reading the other answers here I came up with the below  which IMHO makes it really clear it s a comment  Especially suitable for in-script usage info    lt  lt        Usage  This script launches a spaceship to the moon  It s doing so by  leveraging the power of the Fifth Element  AKA Leeloo  Will only work if you re Bruce Willis or a relative of Milla Jovovich          As a programmer  the sequence of slashes immediately registers in my brain as a comment  even though slashes are normally used for line comments    Of course         is just a string  the number of slashes in the prefix and the suffix must be equal

[shell] Way to create multiline comments in Bash?

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