Programmer Guide/Command Reference/COND

The COND command performs a conditional assignment.

Generally, the conditional assignment takes the following form:

target := COND condition ? expr1 : expr2

target

is a normal assignment target, usually the name of an S_TOOLS-STx variable, e.g. #var.

condition

is a conditional expression like used with the IF statement and the miscellaneous loop commands, e.g. the string $#a == 7 || $#a == 42 (for more examples, see the IF statement).

Note that with conditional S_TOOLS-STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both $#a == 7 and '$#a'=='7' are valid expression, whereas $#a==7 is not.

expr1 and expr2

Both expr1 and expr2 may be any expressions that may be normally used in an S_TOOLS-STx := assignment, with the only exception of a COND expression (meaning that conditional assignments must not be nested for the time being). If, at runtime, the conditional expression condition evaluates to truth, the value determined by the first expression, expr1, will be assigned to target. If condition evaluates to falsehood, it will be the second expression, expr2, that gets assigned to target.

You may use any S_TOOLS-STx conditional expression you like for condition. Equally, there is no restriction on expr1 and expr2, except that they must not be built up from COND expressions themselves. It is even (and also) possible to use command substitutions ($(...)), nesting them as deeply as one feels inclined to.

Notes

• The COND command is processed by the loader, and is therefore not available in the command line interface.
• The COND command may not contain a nested COND command.

Examples

#min := cond $#a < $#b ? $#a : $#b                           // calculate minimum of #a and #b
#abs := cond $#a < 0 ? num -$#a : $#a                        // calculate absolute value of #a
#abs := cond $#a < 0 ? eval $#a*(-1) : $#a                   // an alternative to the above
#absdiff := cond $#a > $#b ? eval $#a-$#b : eval $#b-$#a     // absolute difference
#len := cond $(length $#a) > 0 ? length $#a : length $#b     // length of #a or, if empty, of #b

See the file conditional_assignment.sts for further working examples.