tt07

unix v7是最后一个广泛发布的研究型UNIX版本

.NH
Strings
.PP
Obviously if a paper contains a large number of occurrences
of an acute accent over a letter `e',
typing
.BD \eo"e\e\'"
for each \*e
would be a great nuisance.
.PP
Fortunately,
.UL troff
provides a way in which you can store an arbitrary
collection of text in a `string',
and thereafter use the string name as a shorthand
for its contents.
Strings are one of several
.UL troff
mechanisms whose judicious use
lets you type a document
with less effort and organize
it
so that extensive format changes
can be made with few editing changes.
.PP
A reference to a string is replaced by whatever
text
the string was defined as.
Strings are defined with the command
.BD .ds .
The line
.P1
\&^ds e \eo"e\e'"
.P2
defines the string
.BD e
to have the value
.BD \eo"e\e\'"
.PP
String names may be either one or two characters long,
and are referred to by
.BD \e*x
for one character names or
.BD \e*(xy
for two character names.
Thus to get
t\*el\*ephone,
given the definition of the string
.BD e
as above,
we can say
t\e*el\e*ephone.
.PP
If a string must begin with blanks, define it as
.P1
\&.ds xx "      text
.P2
The double quote signals the beginning of the definition.
There is no trailing quote;
the end of the line terminates the string.
.PP
A string may actually be several lines long;
if
.UL troff
encounters a 
.BD \e
at the end of
.ul
any
line, it is thrown away and the next line
added to the current one.
So you can make a long string simply by ending each line
but the last with a backslash:
.P1
\&^ds xx this \e
is a very \e
long string
.P2
.PP
Strings may be defined in terms of other strings, or even in terms of themselves;
we will discuss some of these possibilities later.