I know that in LaTeX newcommand is defined as:
\newcommand{name}[num] {definition } But I want to define a new command whose argument is not defined between brackets, and it is defined with between \begin and \end commands. For example, something like this:
\teststart bla-bla-bla \testend Maybe I should define two newcommands, one for \teststart and one for \testend.
I should mention that I have seen such commands in the changebar package, \cbstart and \cbend.
A higher level possibility is with xparse:
\usepackage{xparse} \NewDocumentCommand{\teststart}{+u{\testend}}{% do something with #1% } The + allows the argument to contain blank lines.
This is possible using TeX's \def, where you require a specific argument text. The argument text includes both the specific sequence to be replaced, as well as the arguments in the form #X (where X is a number from 1 through 9):
\documentclass{article} \def\teststart#1\testend{left-#1-right} \begin{document} \teststart this is something \testend \end{document} If you want to allow for paragraph breaks between \teststart and \testend, then you need to make the definition using \long
\documentclass{article} \long\def\teststart#1\testend{left-#1-right} \begin{document} \teststart this is something \testend \end{document} You can define an environment this way:
\newenvironment{test}{<commands to execute at beginning}{<commands for end} You use the environment like this:
\begin{test} bla-bla-bla \end{test} If you want to apply a command to the contents of the environment as a whole, you can do this with the environ package. The macro \BODY stands for the whole body of the environment, so you can apply a command to it.
\usepackage{environ} \NewEnviron{test}{<before>\dosomethingtobody{\BODY}<after>} 
xparse, I think. Perhaps this should be a new question? And for contrast, a rather more low-level approach is as follows:
\documentclass{article} \newcommand\teststart{% \begingroup % start a group \bfseries % make the content bold, for demo purposes \let\testend\endgroup % within this 'environment' (only), % \testend acts to close the group } \begin{document} Here is some text, \teststart which has test content\testend within it. And that content \teststart can go over multiple paragraphs. For example.\testend \end{document} This is broadly similar to the way that the \begin{env}...\end{env} mechanism works.
The commands \begingroup and \endgroup create and terminate a group without using {...} (which could not, of course, appear unbalanced within a definition).
\newcommand\teststart[1]{\begingroup \bfseries Test #1: \let\testend\endgroup} was going to be an exercise for the reader... Was being able to manipulate the text between \teststart ...\testend a requirement? Hmm: maybe so. In that case, @Werner's or your solutions would indeed be necessary.