什么是这个bash重定向运算符？ “<

Question

I saw the following bash code: at 19:00 <<! echo "job 1" at 19:00 <<! echo "job 1" . I have two problems:

1. What's this redirection operator: <<! ?

2. I wrote the following script code:

    at 19:00 <<! echo "job 1" at 20:00 <<! echo "job 2" 

   When I executed this script, atq command only showed one job, the first one. What's the matter? And how should I submit the two jobs via this script correctly?

Answer 1

From bash reference manual

3.6.6 Here Documents

This type of redirection instructs the shell to read input from the current source until a line containing only word (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command.

The format of here-documents is: 
     <<[−]word
             here-document
     delimiter

So

1. You shouldn't need to specify anything after word (in your case ! )
2. Then you should specify at job on one or more lines
3. Finally, add a line containing word (again, in your case ! )

Answer 2

The <<! is a here document , as Nya explained.

You should write:

at 19:00 <<!
    echo "job 1"
!
at 20:00 <<!
    echo "job 2"
!

Without the lines starting ! , your here document was the rest of the shell script, which is why there was only one command in the atq . (But, the command would have scheduled the second job when it ran!)