How to both display a command line's output on console and save the output into a text file?

You can use the tee command to accomplish this.

sudo apt-get install someapp 2>&1 | tee ~/someappInstall.txt

Look here for more info, or execute man tee

Note: As others have mentioned, 2>&1 is necessary to redirect STDERR to STDOUT to catch any errors. See this StackOverflow question for a good explanation of what 2>&1 actually does.

tee will do the job as required.

To capture the output into a file, use:

sudo apt-get install your_software | tee log_file.txt

This will only capture the output, but not any error messages. If you would also like to record error messages, modify the command to be:

sudo apt-get install your_software 2>&1  | tee log_file.txt

One of the beauty of apt-get (and APT in general) is that they store log files for almost everything, even the terminal output of any command that you run trough, in the /var/log/apt. For example, this is the last entry in my /var/log/apt/term.log:

Log started: 2014-06-20  16:46:08
(Reading database ... 252472 files and directories currently installed.)
Removing xdotool (1:3.20130111.1-3.1) ...
Processing triggers for man-db (2.6.7.1-1) ...
Log ended: 2014-06-20  16:46:33

Now, comparing with the actual output:

➜  ~  sudo apt-get remove xdotool 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  libxdo3
Use 'apt-get autoremove' to remove it.
The following packages will be REMOVED:
  xdotool
0 upgraded, 0 newly installed, 1 to remove and 2 not upgraded.
After this operation, 135 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 252472 files and directories currently installed.)
Removing xdotool (1:3.20130111.1-3.1) ...
Processing triggers for man-db (2.6.7.1-1) ...

It saved me several lines that are not relevant in most cases, and it does automatically. So, you don't need any extra command to do what you want to do, apt-get does it for you.

try tee command. You can found here some examples.

Simple usage:

  <command> | tee file

example:

  ls | tee outputFile