How to export all Bash functions in a file in one line?

What you should really do is source the file containing the functions inside the script itself, that way it won’t be context-dependent (or rather, it will be less context-dependent).

You could try something like:

declare -fx $(bash -c 'source /path/to/my-file &> /dev/null; compgen -A function')

Since you want to export only functions from the file, sourcing it in a new instance of bash and then using compgen -A function will list names of all the functions defined in that file (and previously exported functions too, but that shouldn't be a problem here). Then you can use the output of that with export -f or declare -fx to export those functions.

As you're sourcing the file in your bashrc, re-sourcing it probably won't be a problem.

Take a look at BASH_ENV

INVOCATION
          When bash is started non-interactively, to  run  a  shell script,  for
          example, it looks for the variable BASH_ENV in the environment, expands
          its value if it appears there, and uses the expanded value as the  name
          of  a  file to read and execute.  Bash behaves as if the following com‐
          mand were executed:
          if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
          but the value of the PATH variable is not used to search for the  file‐
          name.

  BASH_ENV
          If  this parameter is set when bash is executing a shell script,
          its value is interpreted as a filename  containing  commands  to
          initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
          subjected to  parameter  expansion,  command  substitution,  and
          arithmetic  expansion  before  being  interpreted as a filename.
          PATH is not used to search for the resultant filename.

When bash execute a shell script non-interactively .bashrc is not read and the function file are not sourced.
If BASH_ENV is set to the name of the function file, this file is read and executed like said in INVOCATION.
So no need to source the function file in each shell script which use the function.

Example to illustrate :

Not Ubuntu but debian-linux 4.14.0-3-amd64 #1 SMP Debian 4.14.17-1 (2018-02-14) x86_64 GNU/Linux with Xfce 4.12

Create a file of functions in your $HOME

cat mesfuncbash

piste ()
{
echo $0 >> ~/lapiste
date >> ~/lapiste
}

Create a script which use the function

cat lescript

#!/bin/bash
echo $0
. ~/mesfuncbash
piste
echo fin

here the script source the function file

Create a laucher to lescript on the Desktop

No need of terminal

execute it.

The file ~/lapiste is updated.

Now remove . ~/mesfuncbash from lescript

execute it

The file ~/lapiste is not updated.

If you run lescript on a terminal

Bash tell you :

line 3: piste: command not found

Now you must set BASH_ENV to the name of the function file.

In debian with xfce, .profile is not read at startup so you can't use it to set BASH_ENV.

You must create a file .xsessionrc in your $HOME.

cat .xsessionrc

export BASH_ENV="$HOME/mesfuncbash"

logout and login, this way .xsessionrc is read at startup

Now, you can execute the laucher on the Desktop and the file ~/lapiste is updated.

The output of set appears to be sorted favorably for extracting all defined functions. It starts with variables and then shows functions, soes:

set |awk '/^[^=()]*\(\)/ {functions=1} functions' > functions.sh

This looks for the first non-assignment (an occurrence of () before the first =) and then says that's okay to print. The second awk stanza uses the default print action when the variable functions is true. The output is saved in functions.sh, which can then be sourced elsewhere.

Just use the env command:

env > /path/to/file