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Any explanation why the comment is echo'ed in the third example?
$ echo a b \
> c # test
a b c
$ echo a b c \
> # test
a b c
$ echo a b c \
> \ # test
a b c # test
$ echo a b c \
> \ # test
a b c
927
In Shell or Bash shell, we can comment on multiple lines using << and name of comment. we start a comment block with << and name anything to the block and wherever we want to stop the comment, we will simply type the name of the comment.
When writing bash scripts, any text after a hash sign ( # ) indicates the start of a comment, and any text after # in the same line does not execute. When using a text editor or IDE, comments are colored differently from the rest of the code.
' # ' in a line of a makefile starts a comment. It and the rest of the line are ignored, except that a trailing backslash not escaped by another backslash will continue the comment across multiple lines.
In bash, # starts a comment only if it is at the beginning of a word. As per this rule, neither of the following two command lines have comments:
$ echo a b c# test
a b c# test
$ echo a b c \ # test
a b c # test
In the first case above, # is part of the word c# and # is not at the beginning.
In the second case above (your case), # is part of the word # (where the first character is a blank and # is the second character). # is not at the beginning and therefore does not start a comment.
Normally, the shell treats a blank as a word separator. By escaping the blank, it loses that special interpretation and becomes just another character.
The use or not of a continuation line does not change this.
From the section entitled Comments in man bash:
a word beginning with # causes that word and all remaining characters on that line to be ignored. [Emphasis added.]
149
Seems like # test is the next word/argument and since comments have to start with # the third command has no comment.
2
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