How can I find where certain bash function is defined?

Turn on debugging. From the Bash manual:

extdebug

If set at shell invocation, or in a shell startup file, arrange to execute the debugger profile before the shell starts, identical to the --debugger option. If set after invocation, behavior intended for use by debuggers is enabled:

• The -F option to the declare builtin (see Bash Builtins) displays the source file name and line number corresponding to each function name supplied as an argument.

Example:

$ bash --debugger
$ declare -Ff quote
quote 143 /usr/share/bash-completion/bash_completion

And indeed:

$ nl -ba /usr/share/bash-completion/bash_completion | sed -n 143,150p
   143  quote()
   144  {
   145      local quoted=${1//\'/\'\\\'\'}
   146      printf "'%s'" "$quoted"
   147  }
   148
   149  # @see _quote_readline_by_ref()
   150  quote_readline()

This is actually more complicated than it appears at first. Which files are read by your shell depends on what type of shell you are currently running. Whether it is interactive or not, whether it is a login or a non-login shell and what combination of the above. To search through all the default files that can be read by the different shells, you can do (change $functionName to the actual name of the function you are looking for):

grep "$functionName" ~/.bashrc ~/.profile ~/.bash_profile ~/.bash.login \
                     ~/.bash_aliases /etc/bash.bashrc /etc/profile \
                     /etc/profile.d/* /etc/environment 2> /dev/null

If that doesn't work, you may be calling a non-default file using . or its alias source. To find such cases, run:

grep -P '(^|\s)(\.|source)\s+' ~/.bashrc ~/.profile ~/.bash_profile \
                               ~/.bash.login ~/.bash_aliases /etc/bash.bashrc \
                               /etc/profile /etc/profile.d/* /etc/environment 2> /dev/null

That probably needs some explanation. The -P enables Perl Compatible Regular Expressions (PCRE) which let us use some fancier regex syntax. Specifically:

• (^|\s): match either the beginning of a line (^) or whitespace (\s).
• (\.|source)\s+ : match either a literal . character (\.) or the word source, but only if they are followed by one or more whitespace characters.

Here's what that gives me on my system:

$ grep -P '(^|\s)(\.|source)\s+' ~/.bashrc ~/.profile ~/.bash_profile \
>                                ~/.bash.login ~/.bash_aliases /etc/bash.bashrc \
>                                /etc/profile /etc/profile.d/* /etc/environment 2> /dev/null
/home/terdon/.bashrc:   . /etc/bashrc
/home/terdon/.bashrc:   . /etc/bash_completion
/home/terdon/.bashrc:. $HOME/scripts/git-prompt.sh
/home/terdon/.bashrc:#  echo -n "$n : "; grep "^CA"  $n |perl -e 'my ($a,$c)=0; while(<>){$c++;next if /cellular_component_unknown/; next if /biological_process/; $a++} print "$a Classes of $c annotated (" . $a*100/$c . ")\n"' 
/etc/bash.bashrc:[ -r /usr/share/bash-completion/bash_completion   ] && . /usr/share/bash-completion/bash_completion
/etc/profile:       test -r "$profile" && . "$profile"
/etc/profile:   . /etc/bash.bashrc
/etc/profile.d/locale.sh:    . "$XDG_CONFIG_HOME/locale.conf"
/etc/profile.d/locale.sh:    . "$HOME/.config/locale.conf"
/etc/profile.d/locale.sh:    . /etc/locale.conf
/etc/profile.d/Z97-byobu.sh:        . /usr/bin/byobu-launch
/etc/profile.d/Z97-byobu.sh:        . /usr/bin/byobu-launch
/etc/profile.d/Z97-byobu.sh:        . /usr/bin/byobu-launch
/etc/profile.d/Z97-byobu.sh:        . /usr/bin/byobu-launch
/etc/profile.d/Z97-byobu.sh:        . /usr/bin/byobu-launch

As you can see, however, this will print the entire matched line. What we are really interested in is the list of file names called, not the line that is calling them. You can get those with this, more complicated, regex:

grep -hPo '(^|\s)(\.|source)\s+\K\S+' ~/.bashrc ~/.profile ~/.bash_profile \
                                      ~/.bash.login ~/.bash_aliases \
                                      /etc/bash.bashrc /etc/profile \
                                      /etc/profile.d/* /etc/environment 2> /dev/null

The -h flag suppresses the printing of the file names where a match was found, which grep does by default when told to search through multiple files. The -o means "only print the matching portion of the line". The extra stuff added to the regex are:

• \K : ignore anything matched up to this point. This is a PCRE trick that lets you use a complex regex to find your match but not include that matched portion when using grep's -o flag.

On my system, the above command will return:

$ grep -hPo '(^|\s)(\.|source)\s+\K\S+' ~/.bashrc ~/.profile ~/.bash_profile \
>                                       ~/.bash.login ~/.bash_aliases \
>                                       /etc/bash.bashrc /etc/profile \
>                                       /etc/profile.d/* /etc/environment 2> /dev/null
/etc/bashrc
/etc/bash_completion
$HOME/scripts/git-prompt.sh
$a*100/$c
")\n"'
/usr/share/bash-completion/bash_completion
"$profile"
/etc/bash.bashrc
"$XDG_CONFIG_HOME/locale.conf"
"$HOME/.config/locale.conf"
/etc/locale.conf
/usr/bin/byobu-launch
/usr/bin/byobu-launch
/usr/bin/byobu-launch
/usr/bin/byobu-launch
/usr/bin/byobu-launch

Note that I happen to have a use of . followed by a space which is not used for sourcing but that's because I have an alias that is calling another language, not bash. That's what gives the weird $a*100/$c and ")\n"' in the output above. But that can be ignored.

Finally, here's how to put all of that together and search for a function name in all default files and all files your default files are sourcing:

grep_function(){
  target="$@"
  files=( ~/.bashrc ~/.profile ~/.bash_profile ~/.bash.login 
         ~/.bash_aliases /etc/bash.bashrc /etc/profile 
         /etc/profile.d/* /etc/environment)
    while IFS= read -r file; do
      files+=( "$file" )
    done < <(grep -hPo '(^|\s)(\.|source)\s+\K\S+'  "${files[@]}" 2>/dev/null)
    for file in "${files[@]}"; do
      ## The tilde of ~/ can break this
      file=$(sed 's|~/|'"$HOME"'/|g' <<<"$file")
      if [[ -e $file ]]; then
        grep -H "$target" -- "$file"
      fi
    done
}

Add those lines to your ~/.bashrc and you can then run (I am using fooBar as an example function name):

grep_function fooBar

For example, if I have this line in my ~/.bashrc:

. ~/a

And the file ~/a is:

$ cat ~/a
fooBar(){
  echo foo
}

I should find it with:

$ grep_function fooBar
/home/terdon/a:fooBar(){

The usual per-user dotfile bash reads is ~/.bashrc. However, it may very well source other files, I for instance like to keep aliases and functions in separate files called ~/.bash_aliases and ~/.bash_functions, which makes finding them much easier. You can search the .bashrc for source commands with:

grep -E '(^\s*|\s)(\.|source)\s' /home/USERNAME/.bashrc

Once you have the list of user-created files you can search them and the user’s .bashrc with a single grep call, e.g. for function foo for my setup:

grep foo /home/USERNAME/.bash{rc,_aliases,_functions}