fmlexpr(1fmli)

fmlexpr -- evaluate arguments as an expression

Synopsis

   fmlexpr arguments

Description

The fmlexpr function evaluates its arguments as an expression. After evaluation, the result is written on the standard output. Terms of the expression must be separated by blanks. Characters special to FMLI must be escaped. Note that 0 is returned to indicate a zero value, rather than the null string. Strings containing blanks or other special characters should be quoted. Integer-valued arguments may be preceded by a unary minus sign. Internally, integers are treated as 32-bit, 2s complement numbers.

The operators and keywords are listed below. Characters that need to be escaped are preceded by \. The list is in order of increasing precedence, with equal precedence operators grouped within {} symbols.

expr \| expr: returns the first expr if it is neither null nor 0, otherwise returns the second expr.
expr \& expr: returns the first expr if neither expr is null or 0, otherwise returns 0.
expr { =, \>, \>=, \<, \<=, != } expr: returns the result of an integer comparison if both arguments are integers, otherwise returns the result of a lexical comparison.
expr { +, - } expr: addition or subtraction of integer-valued arguments.
expr { , /, % } expr: multiplication, division, or remainder of the integer-valued arguments.
expr : expr: The matching operator : compares the first argument with the second argument which must be a regular expression. Regular expression syntax is the same as that of ed(1), except that all patterns are ``anchored'' (that is, begin with ^) and, therefore, ^ is not a special character, in that context. Normally, the matching operator returns the number of bytes matched (0 on failure). Alternatively, the $ . . . $ pattern symbols can be used to return a portion of the first argument.

Examples

1.

Add 1 to the variable a:

   	`fmlexpr $a + 1 | set -l a`

2.

For $a equal to either ``/usr/abc/file'' or just ``file'':

   	fmlexpr  $a  :  './\(.\)'  \|  $a

returns the last segment of a path name (for example, file). Watch out for / alone as an argument: fmlexpr will take it as the division operator (see NOTICES below).

3.

A better representation of example 2.

   	fmlexpr  //$a  :  './\(.\)'

The addition of the // characters eliminates any ambiguity about the division operator (because it makes it impossible for the left-hand expression to be interpreted as the division operator), and simplifies the whole expression.

4.

Return the number of characters in $VAR.

   	fmlexpr $VAR : .*

Diagnostics

As a side effect of expression evaluation, fmlexpr returns the following exit values:

0: if the expression is neither null nor 0 (that is, TRUE)
1: if the expression is null or 0 (that is, FALSE)
2: for invalid expressions (that is, FALSE).

``syntax error'': for operator/operand errors
``non-numeric argument'': if arithmetic is attempted on such a string

In the case of syntax errors and non-numeric arguments, an error message will be printed at the current cursor position. Use refresh to redraw the screen.

Notices

After argument processing by FMLI, fmlexpr cannot tell the difference between an operator and an operand except by the value. If $a is an =, the command:

   fmlexpr  $a  =  '='

looks like:

   fmlexpr  =  =  =

as the arguments are passed to fmlexpr (and they will all be taken as the = operator). The following works, and returns TRUE:

   fmlexpr  X$a  =  X=

References

ed(1), expr(1), set(1fmli), sh(1)