GNU Info

(groff)Environments

---

Next: Suppressing output Prev: Diversions Up: gtroff Reference

---

Enter node , (file) or (file)node

Environments
============

   It happens frequently that some text should be printed in a certain
format regardless of what may be in effect at the time, for example, in
a trap invoked macro to print headers and footers.  To solve this
`gtroff' processes text in "environments".  An environment contains
most of the parameters that control text processing.  It is possible to
switch amongst these environments; by default `gtroff' processes text
in environment 0.  The following is the information kept in an
environment.

   * font parameters (size, family, style, character height and slant,
     space and sentence space size)

   * page parameters (line length, title length, vertical spacing, line
     spacing, indentation, line numbering, hyphenation data)

   * fill and adjust mode

   * tab stops, tab and leader characters, escape character, no-break
     and hyphen indicators, margin character data

   * partially collected lines

   These environments may be given arbitrary names (see Note:
Identifiers, for more info).  Old versions of `troff' only had
environments named `0', `1' and `2'.

 - Request: .ev env
 - Register: \n[.ev]
     Switches to another environment.  The argument ENV is the name of
     the environment to switch to.  With no argument, `gtroff' switches
     back to the previous environment.  There is no limit on the number
     of named environments; they are created the first time that they
     are referenced.  The `.ev' read-only register contains the name or
     number of the current environment.  This is a string-valued
     register.

     Note that a call to `ev' (with argument) pushes the previously
     active environment onto a stack.  If, say, environments `foo',
     `bar', and `zap' are called (in that order), the first `ev'
     request without parameter switches back to environment `bar'
     (which is popped off the stack), and a second call switches back
     to environment `foo'.

     Here is an example:


          .ev footnote-env
          .fam N
          .ps 6
          .vs 8
          .ll -.5i
          .ev
          
          ...
          
          .ev footnote-env
          \(dg Note the large, friendly letters.
          .ev


 - Request: .evc env
     Copies the environment ENV into the current environment.