Bash Shell comments several ways to _linux shell

1, the simplest way

Copy Code code as follows:

: <<block
.... Comment Content
Block

The input is redefined to the previous command, but: it is an empty command, so it is equivalent to a comment.
If a command with an inverted quotation mark is an error in the annotation, the inverted quotation marks are not commented out, for example, var= ' ls-l ' will not be commented out.

2, solve the problem of the comments have inverted quotes

A, method one

Copy Code code as follows:

: <<block '
.... Comment Content
' Block

B, Method two

Copy Code code as follows:

:<< ' Block
.... Comment Content
Block '

C, Method Three

Copy Code code as follows:

:<< '
.... Comment Content
'

Block for here Documents in the definition of the symbol, the name of any, as long as the match before and after the line.

3.: Instructions and here Documents
: Is not doing anything (do nothing) that is empty command, generally used in if...then ... In a condition, as a command to do nothing, such as:

Copy Code code as follows:

If [-D $DIRECTORY]; Then
:
Else
Echo ' Directory does not exit! '
Fi

The following example:

Copy Code code as follows:

Cmd<<word
Any input
File content
Word

Is the use of here Documents, meaning to pass the above definition Word to a script or command.
Word's content is to enter anything between two words, so that you can use CMD in the script to perform the input without rebuilding a file.

Here Documents are commonly used in menu screens, such as:

Copy Code code as follows:

Cat <<menu
1.List
2.Help
3.Exit
Menu

As for

Copy Code code as follows:

: <<word
.... Comment Content
Word

It's similar to building a local file and then executing an empty command on it, doing nothing, which is equivalent to commenting.

Add:

The code is as follows:

Copy Code code as follows:

for ((i=0; i<10; i++))
Todo
: <<_a_
if []; Then
...
Fi
_a_
echo ""
Done

Above: <<_a_ and _a_ represent segment annotation, you can comment out the middle code

_a_ is the definition symbol in here Documents, the name is arbitrary, as long as the match on the line

: Empty command, which is equivalent to doing nothing (doing anything) is an empty command, generally used in if...then ... In a condition, as a command to do nothing, such as:

Copy Code code as follows:

If [-D $DIRECTORY]; Then
:
Else
Echo ' Directory does not exit! '
Fi

If a command with an inverted quotation mark is an error in the annotation, the inverted quotation marks are not commented out, for example, var= ' ls-l ' will not be commented out.

Troubleshoot problems with inverted quotes in comments

Copy Code code as follows:

: <<_a_ '
.... Comment Content
' _a_

A single line will not be said, the well number # can be done. Here are a few lines.

A. Through here documents to achieve:

1)
: <<eof
The code for the annotation ...
Eof
Colon: means doing nothing.
Description: When a variable reference or inverted quotation mark appears in the annotation code, bash tries to parse them and prompts for an error message. There are several ways to fix this:

1.

Copy Code code as follows:

: <<\eof
The code for the annotation ...
Eof

2.

Copy Code code as follows:

:<< ' EOF '
The code for the annotation ...
Eof

3.

Copy Code code as follows:

:<< ' EOF
The code for the annotation ...
EOF '

4.

Copy Code code as follows:

: <<eof '
The code for the annotation ...
' EOF

5.

Copy Code code as follows:

:<< '
The code for the annotation ...
'