Programmer Guide/Command Reference/COND: Difference between revisions
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;<var>condition</var>: is a [[Programmer_Guide/Introduction#Conditional_Expressions|conditional expression]] like used with the <code>[[Programmer_Guide/Command_Reference|IF]]</code> statement and the miscellaneous conditional [[Programmer_Guide/Introduction#Control_Commands|control commands]]. | ;<var>condition</var>: is a [[Programmer_Guide/Introduction#Conditional_Expressions|conditional expression]] like used with the <code>[[Programmer_Guide/Command_Reference|IF]]</code> statement and the miscellaneous conditional [[Programmer_Guide/Introduction#Control_Commands|control commands]]. | ||
::*Note that with conditional {{STX}} expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both <code>$#a == 7</code> and <code>'$#a'=='7'</code> are valid expression, whereas <code>$#a==7</code> is not. | ::*Note that with conditional {{STX}} expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both <code>$#a == 7</code> and <code>'$#a'=='7'</code> are valid expression, whereas <code>$#a==7</code> is not. | ||
;<var>expr1</var> and <var>expr2</var>: Both <code>expr1</code> and <code>expr2</code> may be any | ;<var>expr1</var> and <var>expr2</var>: Both <code>expr1</code> and <code>expr2</code> may be any commands, with the only exception of all control commands. If, at runtime, the conditional expression <var>condition</var> evaluates to truth, the value the first command <var>expr1</var> will be executed, otherwise the second <var>expr2</var>. If <var>target</var> is specified, the return value of the executed command is assigned. | ||
==Notes== | |||
* The <code>COND</code> command is processed by the loader, and is therefore not available in the command line interface. | * The <code>COND</code> command is processed by the loader, and is therefore not available in the command line interface. | ||
* The <code>COND</code> command may not contain a nested <code>COND</code> command. | * The <code>COND</code> command may not contain a nested <code>COND</code> command. | ||
==See also== | |||
conditonal assignment with [[../EVAL|EVAL]], [[Programmer_Guide/Introduction#Control_Commands|control commands]], [[../IF|IF]] | |||
=== Examples === | === Examples === | ||
#min := cond $#a < $#b ? $#a : $#b // calculate minimum of #a and #b | #min := cond $#a < $#b ? $#a : $#b // calculate minimum of #a and #b | ||
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See the file <code>conditional_assignment.sts</code> for further working examples. | See the file <code>conditional_assignment.sts</code> for further working examples. | ||
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Revision as of 15:45, 27 April 2011
The COND command performs a conditional assignment.
Contents
Usage
[ target := ] COND condition ? expr1 : expr2
- target
- is a normal assignment target, usually the name of an STx variable, e.g.
#var. If no target is specified, a conditional execution is performed. - condition
- is a conditional expression like used with the
IFstatement and the miscellaneous conditional control commands.- Note that with conditional STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both
$#a == 7and'$#a'=='7'are valid expression, whereas$#a==7is not.
- Note that with conditional STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both
- expr1 and expr2
- Both
expr1andexpr2may be any commands, with the only exception of all control commands. If, at runtime, the conditional expression condition evaluates to truth, the value the first command expr1 will be executed, otherwise the second expr2. If target is specified, the return value of the executed command is assigned.
Notes
- The
CONDcommand is processed by the loader, and is therefore not available in the command line interface. - The
CONDcommand may not contain a nestedCONDcommand.
See also
conditonal assignment with EVAL, control commands, IF
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.
