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unix v7是最后一个广泛发布的研究型UNIX版本

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.rm mx
.mh
Tabs, Leaders, and Fields
.sc
Tabs and leaders.
The \s-1ASCII\s+1 horizontal tab character and the \s-1ASCII\s+1
\s-1SOH\s+1 (hereafter known as the \fIleader\fR character)
can both be used to generate either horizontal motion or
a string of repeated characters.
The length of the generated entity is governed
by internal \fItab stops\fR specifiable
with \fBta\fR.
The default difference is that tabs generate motion and leaders generate
a string of periods;
\fBtc\fR and \fBlc\fR
offer the choice of repeated character or motion.
There are three types of internal tab stops\(em\
\fIleft\fR adjusting, \fIright\fR adjusting,
and \fIcentering\fR.
In the following table:
\fID\fR is the distance from the current position on the \fIinput\fR line
(where a tab or leader was found)
to the next tab stop;
\fInext-string\fR consists
of the input characters following the tab (or leader) up to the next tab (or leader) or end of line;
and
\fIW\fR is the width of \fInext-string\fR.
.TS
center box;
c2|c2|c
c2|c2|c
c2|c2|l.
Tab	Length of motion or	Location of
type	repeated characters	\fInext-string\fR
_
Left	\fID\fR	Following \fID\fR
Right	\fID\-W\fR	Right adjusted within \fID\fR
Centered	\fID\-W\(sl\fR2	Centered on right end of \fID\fR
.TE
The length of generated motion is allowed to be negative, but
that of a repeated character string cannot be.
Repeated character strings contain an integer number of characters, and
any residual distance is prepended as motion.
Tabs or leaders found after the last tab stop are ignored, but may be used
as \fInext-string\fR terminators.
.pg
Tabs and leaders are not interpreted in \fIcopy mode\fR.
\fB\et\fR and \fB\ea\fR always generate a non-interpreted
tab and leader respectively, and
are equivalent to actual tabs and leaders in \fIcopy mode\fR.
.sc
Fields.
A \fIfield\fR is contained between
a \fIpair\fR of \fIfield delimiter\fR characters,
and consists of sub-strings
separated by \fIpadding\fR indicator characters.
The field length is the distance on the
\fIinput\fR line from the position where the field begins to the next tab stop.
The difference between the total length of all the sub-strings
and the field length is incorporated as horizontal
padding space that is divided among the indicated
padding places.
The incorporated padding is allowed to be negative.
For example,
if the field delimiter is \fB#\fR and the padding indicator is \fB^\fR,
\fB#^\fIxxx\fB^\fIright\|\fB#\fR
specifies a right-adjusted string with the string \fIxxx\fR centered
in the remaining space.
.h1
.bt
\fB&ta\fI|Nt|...\fR	0.8;|0.5in	none	E,\fBm\fR	\
Set tab stops and types.
\fIt=\fBR\fR, right adjusting;
\fIt=\fBC\fR, centering;
\fIt\fR absent, left adjusting.
\*(TR tab stops are preset every 0.5in.;
\*(NR every 0.8in.
The stop values are separated by spaces, and
a value preceded by \fB+\fR
is treated as an increment to the previous stop value.
.bt
\fB&tc\fI|c\fR	none	none	E	\
The tab repetition character becomes \fIc\fR,
or is removed specifying motion.
.bt
\fB&lc\fI|c\fR	\fB.\fR	none	E	\
The leader repetition character becomes \fIc\fR,
or is removed specifying motion.
.bt
\fB&fc\fI|a|b\fR	off	off	-	\
The field delimiter is set to \fIa\fR;
the padding indicator is set to the \fIspace\fR character or to
\fIb\fR, if given.
In the absence of arguments the field mechanism is turned off.
.mh
Input and Output Conventions and Character Translations
.sc
Input character translations.
Ways of inputting the graphic character set were
discussed in \(sc2.1.
The \s-1ASCII\s+1 control characters horizontal tab (\(sc9.1),
\s-1SOH\s+1 (\(sc9.1), and backspace (\(sc10.3) are discussed elsewhere.
The newline delimits input lines.
In addition,
\s-1STX\s+1, \s-1ETX\s+1, \s-1ENQ\s+1, \s-1ACK\s+1, and \s-1BEL\s+1
are accepted,
and may be used as delimiters or translated into a graphic with \fBtr\fR (\(sc10.5).
\fIAll\fR others are ignored.
.pg
The \fIescape\fR character \fB\e\fR
introduces \fIescape sequences\fR\(em\
causes the following character to mean
another character, or to indicate
some function.
A complete list of such sequences is given in the Summary and Index on page 6.
\fB\e\fR
should not be confused with the \s-1ASCII\s+1 control character \s-1ESC\s+1 of the
same name.
The escape character \fB\e\fR can be input with the sequence \fB\e\e\fR.
The escape character can be changed with \fBec\fR,
and all that has been said about the default \fB\e\fR becomes true
for the new escape character.
\fB\ee\fR can be used to print whatever the current escape character is.
If necessary or convenient, the escape mechanism may be turned off with \fBeo\fR,
and restored with \fBec\fR.
.h1
.bt
\fB&ec\fI|c\fR	\fB\e\fR	\fB\e\fR	-	\
Set escape character to \fB\e\fR, or to \fIc\fR, if given.
.bt
\fB&eo\fR	on	-	-	Turn escape mechanism off.
.sc
Ligatures.
.lg0
Five ligatures are available
in the current \*(TR character set \(em
\fB\(fi\fR, \fB\(fl\fR, \fB\(ff\fR, \fB\(Fi\fR, and \fB\(Fl\fR.
They may be input (even in \*(NR) by
\fB\e(fi\fR, \fB\e(fl\fR, \fB\e(ff\fR, \fB\e(Fi\fR, and \fB\e(Fl\fR respectively.
.lg
The ligature mode is normally on in \*(TR, and \fIautomatically\fR invokes 
ligatures during input.
.h1
.bt
\fB&lg\fI|N\fR	off;|on	on	-	Ligature mode
is turned on if \fIN\fR is absent or non-zero,
and turned off if \fIN\(eq\^\fR0.
If \fIN\fR\(eq\^2, only the two-character ligatures are automatically invoked.
Ligature mode is inhibited for
request, macro, string, register, or file names,
and in \fIcopy mode\fR.
No effect in \*(NR.
.sc
Backspacing, underlining, overstriking, etc.
Unless in \fIcopy mode\fR, the \s-1ASCII\s+1 backspace character is replaced
by a backward horizontal motion having the width of the
space character.
Underlining as a form of line-drawing is discussed in \(sc12.4.
A generalized overstriking function is described in \(sc12.1.
.pg
\*(NR automatically underlines
characters in the \fIunderline\fR font,
specifiable with \fBuf\fR,
normally that on font position 2 (normally Times Italic, see \(sc2.2).
In addition to \fBft\fR and \fB\ef\fIF\fR,
the underline font may be selected by \fBul\fR and \fBcu\fR.
Underlining is restricted to an output-device-dependent
subset of \fIreasonable\fR characters.
.h1
.bt
\fB&ul\fI|N\fR	off	\fIN\(eq\fR1	E	\
Underline in \*(NR (italicize in \*(TR) the next \fIN\fR
input text lines.
Actually, switch to \fIunderline\fR font, saving the
current font for later restoration;
\fIother\fR font changes within the span of a \fBul\fR
will take effect,
but the restoration will undo the last change.
Output generated by \fBtl\fR (\(sc14) \fIis\fR affected by the
font change, but does \fInot\fR decrement \fIN\fR.
If \fIN\fR\^>\^1, there is the risk that
a trap interpolated macro may provide text
lines within the span;
environment switching can prevent this.
.bt
\fB&cu\fI|N\fR	off	\fIN\(eq\fR1	E	\
A variant of \fBul\fR that causes \fIevery\fR character to be underlined in \*(NR.
Identical to \fBul\fR in \*(TR.
.bt
\fB&uf\fI|F\fR	Italic	Italic	-	\
Underline font set to \fIF\fR.
In \*(NR,
\fIF\fR may \fInot\fR be on position 1 (initially Times Roman).
.sc
Control characters.
Both the control character \fB.\fR and the \fIno-break\fR
control character \fB\'\fR may be changed, if desired.
Such a change must be compatible with the design
of any macros used in the span of the change,
and
particularly of any trap-invoked macros.
.h1
.bt
\fB&cc\fI|c\fR	\fB.\fR	\fB.\fR	E	\
The basic control character is set to \fIc\fR,
or reset to "\fB.\fR".
.bt
\fB&c2\fI|c\fR	\fB\'	\'\fR	E	The \fInobreak\fR control character is set
to \fIc\fR, or reset to "\fB\'\fR".
.sc
Output translation.
One character can be made a stand-in for another character using \fBtr\fR.
All text processing (e. g. character comparisons) takes place
with the input (stand-in) character which appears to have the width of the final
character.
The graphic translation occurs at the moment of output
(including diversion).
.h1
.bt
\fB&tr\fI|abcd....\fR	none	-	O	Translate \
\fIa\fR into \fIb\fR, \fIc\fR into \fId\fR, etc.
If an odd number of characters is given,
the last one will be mapped into the space character.
To be consistent, a particular translation
must stay in effect from \fIinput\fR to \fIoutput\fR time.
.sc
Transparent throughput.
An input line beginning with a \fB\e!\fR is read in \fIcopy mode\fR and \fItransparently\fR output
(without the initial \fB\e!\fR);
the text processor is otherwise unaware of the line's presence.
This mechanism may be used to pass control information to a post-processor
or to imbed control lines in a macro created by a diversion.
.sc
Comments and concealed newlines.
An uncomfortably long input line that must stay
one line (e. g. a string definition, or nofilled text)
can be split into many physical lines by ending all but
the last one with the escape \fB\e\fR.
The sequence \fB\e\fR(newline) is \fIalways\fR ignored\(em\
except in a comment.
Comments may be imbedded at the \fIend\fR of any line by