Through gnuplot version 4.4, the scope of the if/else commands was limited to a single input line. This has been replaced by allowing a multi-line clause to be enclosed in curly brackets. The old syntax is still honored by itself but cannot be used inside a bracketed clause.
If no opening "{" follows the `if` keyword, the command(s) in <command-line> will be executed if <condition> is true (non-zero) or skipped if <condition> is false (zero). Either case will consume commands on the input line until the end of the line or an occurrence of `else`. Note that use of `;` to allow multiple commands on the same line will _not_ end the conditionalized commands.
Examples:
pi=3 if (pi!=acos(-1)) print "?Fixing pi!"; pi=acos(-1); print pi
will display:
?Fixing pi! 3.14159265358979
but
if (1==2) print "Never see this"; print "Or this either"
will not display anything.
else:
v=0 v=v+1; if (v%2) print "2" ; else if (v%3) print "3"; else print "fred"
(repeat the last line repeatedly!)
See reread for an example of using if and reread together to perform a loop.