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 30 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.

Usage

Expressions

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 : (colon) 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

Example 1 Incrementing a variable

Add 1 to the variable a:

example% fmlexpr  $a  +  1 | set -l a

Example 2 Setting a variable equal to a filename

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

example% fmlexpr $a : .*/\(.*\) \| $a

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

Example 3 A better representation of Example 2

example% 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.

Example 4 Counting characters in a variable

Return the number of characters in $VAR:

example% fmlexpr $VAR : .*

Exit Status

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).

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

ed(1), expr(1), set(1F), sh(1), attributes(5)

Diagnostics

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.

Notes

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:

example% fmlexpr $a = =

looks like:

example% fmlexpr = = =

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

example% fmlexpr X$a = X=