Myujth

How to include the redirected command itself to the output file redirection? For example

echo "hello!">output.txt

I want the content of output file like this:

echo "hello!">output.txt
hello!

You may want one of two things here.

1. 
   

   Using tee to get the result of the echo sent to the terminal as well as to the file:

   
   
   

   $ echo 'hello!' | tee output
   hello!
   $ cat output
   hello!
   

   
   


2. 
   

   Using script to capture the whole terminal session:

   
   
   

   $ script
   Script started, output file is typescript
   $ echo 'hello!' >output
   $ cat output
   hello!
   $ exit
   Script done, output file is typescript
   

   
   
   
   
   

   $ cat typescript
   Script started on Sat Nov 10 15:15:06 2018
   $ echo 'hello!' >output
   $ cat output
   hello!
   $ exit
   
   Script done on Sat Nov 10 15:15:37 2018
   

   
   

If this is not what you are asking for, then please clarify your question.

In the genearality you're asking for, this is not possible.

To achieve this with additional tools (akin to script(1)), it would be necessary for that program, observing your shell, that in

command >foo

foo is the name of a file, and create it. Also, the shell would try to create it, so there's conflict already. Also, what if the program would print

command >foo

to the terminal?

From inside the shell, well, the shell's redirection process is extremely primitive from a programming point of view (try to find a C lecture where they build a primitive shell themselves, it is really surprising).

If you really need this, you would have to hack your own shell to intercept redirections and pass the command into the target file. But there are probably a lot of nasty issues in the details...

You can also pipe the whole shell:

$ sh -i |& tee sh.log
sh-4.4$ hello
sh: hello: command not found
sh-4.4$ echo hi
hi
sh-4.4$ exit

-i is needed to keep the shell interactive despite stdout not being a terminal. bash and zsh also support that option. |& pipes stdout and stderr; it works with zsh and bash, but not sh (there, you'd need 2>&1 |). Of course, you could also use &> or 2>&1 > if you just want to redirect to a file and nothing more. Anyways, sh.log here contains everything.

$ cat sh.log
sh-4.4$ hello
sh: hello: command not found
sh-4.4$ echo hi
hi
sh-4.4$ exit

If it's acceptable for you to drop the output filename, I think the following is the easiest way:

command='echo "hello!"'
(echo "$command"; eval "$command") >output.txt

But if you need to print the filename then you could use the following:

command='echo "hello!"'
(echo "$command >output.txt"; eval "$command") >output.txt

You can introduce a variable for the filename in order to make sure that it is the same in the two occurrences:

output="output.txt"
command='echo "hello!"'
(echo "$command >$output"; eval "$command") >$output

This way you avoid the risk of having a difference in the printed filename and the actual filename.