How can I automatically prepend a prompt (e.g. $) to each line of a listing?

Question

I have something that looks as follows:

\documentclass{article}
\usepackage{listings}

\lstnewenvironment{shellsession}[1][]
{\lstset{language=bash,
    basicstyle=\small\ttfamily,
    numbers=none,
    #1
  }}
{}

\begin{document}
\begin{shellsession}
  first line
  second line
  third line
\end{shellsession}
\end{document}

This gives me the following output:

No surprises there, but I'm wondering whether there is a way to prepend a character to each line. Just to be clear, the output I'd like to get is

$ first line
$ second line
$ third line

Answer 1

You can prepend something to every "real" line (i.e. not a line created by listings's breaklines option) via a listings hook called EveryPar.

Note that, because listings hooks are global, some precautions must be taken if you're typesetting code in multiple listings languages but you only want to prepend stuff to lines of listings in a subset of those languages (only one, bash, here).

Also, be aware that, without using any countermeasures, e.g.

• listings's gobble option (see the bottom of section 4.4 in the listings manual)
• Martin Scharrer's lstautogobble package, or
• my experimental lstautodedent package,

any indentation present in your listing environment will be typeset in the output; this may end up "pushing" your listing to the right, which is undesirable.

\documentclass{article}
\usepackage{listings}

\makeatletter

% define custom macro that expands to the language name
% (for comparison purposes)
\newcommand\langname@bash{}
\def\langname@bash{bash}

% define custom prompt
\newcommand\prompt@bash{\$\ }

% define a macro (initially empty) and insert it at the beginning
% of every paragraph
\newcommand\addedToEveryPar@bash{}
\lst@AddToHook{EveryPar}{\addedToEveryPar@bash}

% redefine the macro by the custom prompt, but only if the language in use
% be `bash'
\lst@AddToHook{PreInit}{%
  \ifx\lst@language\langname@bash%
    \let\addedToEveryPar@bash\prompt@bash%
  \fi
}

\makeatother


\lstnewenvironment{shellsession}[1][]
{\lstset{language=bash,
    basicstyle=\small\ttfamily,
    numbers=none,
    #1
  }}
{}

\begin{document}
\begin{shellsession}
first line
second line
third line
\end{shellsession}

% just to check that your prompt doesn't find its way into unrelated language...
% (code taken from http://stackoverflow.com/a/14560801/2541573)
\begin{lstlisting}[language=Python, basicstyle=\ttfamily]
def memo(f):
    cache = {}
    def memoized(n):
        nonlocal cache
        if n not in cache:
            cache[n] = f(n)
        return cache[n]
    return memoized
\end{lstlisting}

\end{document}