GNU Info

(groff)if-else

---

Next: while Prev: Operators in Conditionals Up: Conditionals and Loops

---

Enter node , (file) or (file)node

if-else
-------

   `gtroff' has if-then-else constructs like other languages, although
the formatting can be painful.

 - Request: .if expr anything
     Evaluate the expression EXPR, and executes ANYTHING (the remainder
     of the line) if EXPR evaluates to non-zero (true).  ANYTHING is
     interpreted as though it was on a line by itself (except that
     leading spaces are swallowed).  Note: Expressions, for more info.


          .nr xxx 1
          .nr yyy 2
          .if ((\n[xxx] == 1) & (\n[yyy] == 2)) true
              => true


 - Request: .ie expr anything
 - Request: .el anything
     Use the `ie' and `el' requests to write an if-then-else.  The
     first request is the `if' part and the latter is the `else' part.


          .ie n .ls 2 \" double spacing in nroff
          .el   .ls 1 \" single spacing in troff


   In many cases, an if (or if-else) construct needs to execute more
than one request.  This can be done using the `\{' and `\}' escapes.
The following example shows the possible ways to use these escapes
(note the position of the opening and closing braces).


     .ie t \{\
     .    ds lq ``
     .    ds rq ''
     .\}
     .el \
     .\{\
     .    ds lq "
     .    ds rq "\}

   Note: Expressions.