Character Translations (The GNU Troff Manual)

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5.13 Character Translations

+ + + +

A translation is a mapping of an input character to an output +glyph. The mapping occurs at output time, i.e., the input character +gets assigned the metric information of the mapped output character +right before input tokens are converted to nodes (see gtroff Internals, for more on this process). +

Request: .tr abcd… ¶

Request: .trin abcd… ¶

Translate character a to glyph b, character c to +glyph d, and so on. If there is an odd number of characters +in the argument, the last one is translated to a fixed-width space (the +same one obtained by the \SP escape sequence). +

The trin request is identical to tr, but when you unformat +a diversion with asciify it ignores the translation. +See Diversions, for details about the asciify request. +

Some notes: +

+ + + + + + + + + + + + +Special characters (\(xx, \[xxx], +\C'xxx', \', \`, \-, \_), +glyphs defined with the char request, and numbered glyphs +(\N'xxx') can be translated also. + +
+The \e escape can be translated also. + +
+ +Characters can be mapped onto the \% and \~ escape +sequences (but \% and \~ can’t be mapped onto another +glyph). + +
+ + + + + + + + + +The following characters can’t be translated: space (with one exception, +see below), backspace, newline, leader (and \a), tab (and +\t). + +
+Translations are not considered for finding the soft hyphen character +set with the shc request. + +
+The pair ‘c\&’ (an arbitrary character c followed +by the dummy character) maps this character to “nothing”. + +
+
```
.tr a\&
+foo bar
+    ⇒ foo br
+
```
+ +
Even the space character can be mapped to the dummy character. +
+
+
```
.tr aa \&
+foo bar
+    ⇒ foobar
+
```
+ +
As shown in the example, the space character can’t be the first +character/glyph pair as an argument of tr. Additionally, it is +not possible to map the space character to any other glyph; requests +like ‘.tr aa x’ undo ‘.tr aa \&’ instead. +
+
If justification is active, lines are justified in spite of the ‘empty’ +space character (but there is no minimal distance, i.e., the space +character, between words). +
+
After an output glyph has been constructed (this happens at the moment +immediately before the glyph is appended to an output glyph list, either +by direct output, in a macro, diversion, or string), it is no longer +affected by tr. + +
Translating character to glyphs where one of them or both are undefined +is possible also; tr does not check whether the elements of its +argument exist. + +
See gtroff Internals. +
+
Without an argument, the tr request is ignored. +

+ +

Request: .trnt abcd… ¶

+ +

trnt is the same as the tr request except that the +translations do not apply to text that is transparently throughput into +a diversion with \!. See Diversions. +

For example, +

.tr ab
+.di x
+\!.tm a
+.di
+.x
+

+ +

prints ‘b’ to the standard error stream; if trnt is used +instead of tr it prints ‘a’. +

+ + + +