Cfrgtkky

To expand on Alan's good answer (and to reiterate his ‘no’) there's another big reason that bf and it are not recommended now: they are short and easy to type, but they do not have semantics. LaTeX attempts to separate content and formatting in its markup, and these font changing commands break such ideals.

In the rough, commands to type often as part of your document should be short and meaningful; commands to define formatting decisions should be long and descriptive.

Following on the markdown idea mentionned in comments by @Emre, it can be coded in LaTeX. For instance, the code below gets *italics* and **bold** to work (with nesting as well).

documentclass{article}

makeatletter

newcommand{star@out}{%

  star@ifnext{bgroupbfseriesletstar@currentstar@inbf@gobble}%

              {bgroupitshapeletstar@currentstar@init}}

newcommand{star@inbf}{%

  star@ifnext{egroup@gobble}{bgroupitshapeletstar@currentstar@initbf}}

newcommand{star@init}{%

  star@ifnext{bgroupbfseriesletstar@currentstar@initbf}{egroup}}

newcommand{star@initbf}{star@ifnext{egroup@gobble}{egroup}}

letstar@currentstar@out



newcommand{star@ifnext}[2]{%

  def reserved@a {#1}%

  def reserved@b {#2}%

  futurelet @let@token star@ifnext@aux 

}

begingroup

catcode`*=13

@firstofone{endgroup

  newcommand{*}{star@current}

  newcommand{star@ifnext@aux}{%

    ifx @let@token *let reserved@c reserved@a 

    else             let reserved@c reserved@b 

    fi 

    reserved@c

  }

}

makeatother



AtBeginDocument{catcode`*=13}





begin{document}



Hello, *th**i**s* is a **test, *to see* whether** it works.



end{document}

EDIT as per Hendrik Vogt's suggestion. The construction

begingroup

catcode`*=13

@firstofone{endgroup ... }

ensures that every * within the argument of @firstofone has catcode 13. Namely, a group is started, in which * are active, then @firstofone does nothing but forces TeX to read its argument, converting characters of the input file to tokens (with catcode fixed, except if someone later uses scantokens), and the group then ends with endgroup. The catcode of * is restored, which means that any * which is read later (i.e., not those in the argument of @firstofone) will be of catcode 12 (other). The advantage of this construction over doing catcode`*=13 before and catcode`*=12 after is that the catcode of * keeps whichever value it had, even if it wasn't 12.

Following the answer of Bruno, the wiki package allow a very simplified entry of
boldface and italics fonts using the Wikipedia syntax:

documentclass{article}

usepackage{wiki}

begin{document}

wikimarkup

Write in '''bold''', ''italic'' or '''''both'''''.

end{document}

Bold and italics can be nested and even overlapped, so that you can obtain the eqivalent to textit{intertextbf{sec}}textbf{tion}
with ''inter'''sec''tion'''.

First, regarding the use of the PlainTeX-based font switching commands rm, sf, tt, etc in a LaTeX document: Even though the LaTeX2e kernel does not define these commands, they are in fact still available if you use one of the "standard" document classes -- article, report, and book -- or a document class that's based on these three classes. For more on how rm, sf, etc are implemented in the article, report, and book classes see, e.g., this answer to the posting Is there any reason not to use let to redefine a deprecated control sequence to the currently recommended one?

Second, here's a solution that uses LuaLaTeX to convert some simple markdown-type text formatting "instructions" into LaTeX code. Specifically, text inside matched pairs of ***, **, and * characters in a line of input is rendered in bold-italics, bold, and italics, respectively.

The operation of the Lua function that does the main work can be initiated and terminated via two LaTeX macros named MarkdownOn and MarkdownOff. The Lua function doesn't operate on material contained in verbatim-like environments.

documentclass{article}



%% Lua-side code

usepackage{luacode}

begin{luacode}

in_verbatim = false

function markdown ( line ) 

-- don't operate on input if we're in a verbabim-type environment

if string.find ( line , "\begin{[vV]erbatim}" ) then

  in_verbatim = true

elseif string.find ( line , "\end{[vV]erbatim}" ) then

  in_verbatim = false

elseif in_verbatim == false then

  line = string.gsub ( line, "%*%*%*(.-)%*%*%*" , "\textbf{\textit{%1}}")

  line = string.gsub ( line, "%*%*(.-)%*%*" ,     "\textbf{%1}")

  line = string.gsub ( line, "%*(.-)%*" ,         "\textit{%1}" )

end

return line

end

end{luacode}



%% TeX-side code

newcommandMarkdownOn{directlua{luatexbase.add_to_callback( 

   "process_input_buffer", markdown, "markdown" )}}

newcommandMarkdownOff{directlua{luatexbase.remove_from_callback( 

   "process_input_buffer", "markdown" )}}



setlengthparindent{0pt} % just for this example



begin{document}

MarkdownOn

Lua function texttt{markdown} turned on:



*italic*, **bold**, ***bold italic***



bigskip

A line inside a texttt{verbatim} environment:



begin{verbatim}

*italic*, **bold**, ***bold italic***

end{verbatim}



bigskip

MarkdownOff

Lua function texttt{markdown} turned off:



*italic*, **bold**, ***bold italic***

end{document}

I had the same problem recently:

scrartcl Error: undefined old font command `bf'.

After some investigations, I found this on the tug.org web site:

makeatletter

DeclareOldFontCommand{rm}{normalfontrmfamily}{mathrm}

DeclareOldFontCommand{sf}{normalfontsffamily}{mathsf}

DeclareOldFontCommand{tt}{normalfontttfamily}{mathtt}

DeclareOldFontCommand{bf}{normalfontbfseries}{mathbf}

DeclareOldFontCommand{it}{normalfontitshape}{mathit}

DeclareOldFontCommand{sl}{normalfontslshape}{@nomathsl}

DeclareOldFontCommand{sc}{normalfontscshape}{@nomathsc}

makeatother

It allows to recover all "old" TeX commands we all like...