Bash中使用多行注释的方法（Here Documents）

2012-10-19 wcdj

在bash脚本中的使用方法：

: << InputComesFromHERE
There are
more  lines
in this bash file
InputComesFromHERE

Example. Multi-line message using cat

#!/bin/bash

#  'echo' is fine for printing single line messages,
#+  but somewhat problematic for for message blocks.
#   A 'cat' here document overcomes this limitation.

cat <<End-of-message
-------------------------------------
This is line 1 of the message.
This is line 2 of the message.
This is line 3 of the message.
This is line 4 of the message.
This is the last line of the message.
-------------------------------------
End-of-message

#  Replacing line 7, above, with
#+   cat > $Newfile <<End-of-message
#+       ^^^^^^^^^^
#+ writes the output to the file $Newfile, rather than to stdout.

exit 0

#--------------------------------------------
# Code below disabled, due to "exit 0" above.

# S.C. points out that the following also works.
echo "-------------------------------------
This is line 1 of the message.
This is line 2 of the message.
This is line 3 of the message.
This is line 4 of the message.
This is the last line of the message.
-------------------------------------"
# However, text may not include double quotes unless they are escaped.

A here document is a special-purpose code block. It uses a form of I/O redirection to feed a command list to an interactive program or a command, such as ftp, cat, or the ex text editor.

COMMAND <<InputComesFromHERE
...
...
...
InputComesFromHERE

注意：
(1) Here Documents的更多使用方法可以参考这里   http://tldp.org/LDP/abs/html/here-docs.html
(2) : 是空命令，结合Here Documents在bash脚本中使用就相当于注释了。