07-02-2007
Quote:
Originally Posted by
jeriryan87
Hi, I'm trying to do something like this: range= `expr `date '+%m'` - 1` and it does not work. How can I tell it to evaluate an expression within another expression evaluation? I was at first worried that `date '+%m'` would return a string but apparently expr does the math okay normally, so the problem is how to get it to evaluate an inner set of backticks within the outer set of backticks. Thanks.
Personally, I agree with Shell_Life - but there is a way to do it.
backslash the inner back ticks - like this:
echo `expr \`date '+%m'\` - 1`
6
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LEARN ABOUT MOJAVE
tcl_exprlong
Tcl_ExprLong(3) Tcl Library Procedures Tcl_ExprLong(3)
__________________________________________________________________________________________________________________________________________________
NAME
Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprString - evaluate an expression
SYNOPSIS
#include <tcl.h>
int
Tcl_ExprLong(interp, expr, longPtr)
int
Tcl_ExprDouble(interp, expr, doublePtr)
int
Tcl_ExprBoolean(interp, expr, booleanPtr)
int
Tcl_ExprString(interp, expr)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in whose context to evaluate expr.
const char *expr (in) Expression to be evaluated.
long *longPtr (out) Pointer to location in which to store the integer value of the expression.
int *doublePtr (out) Pointer to location in which to store the floating-point value of the expression.
int *booleanPtr (out) Pointer to location in which to store the 0/1 boolean value of the expression.
_________________________________________________________________
DESCRIPTION
These four procedures all evaluate the expression given by the expr argument and return the result in one of four different forms. The
expression can have any of the forms accepted by the expr command. Note that these procedures have been largely replaced by the object-
based procedures Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, and Tcl_ExprObj. Those object-based procedures evaluate an
expression held in a Tcl object instead of a string. The object argument can retain an internal representation that is more efficient to
execute.
The interp argument refers to an interpreter used to evaluate the expression (e.g. for variables and nested Tcl commands) and to return
error information.
For all of these procedures the return value is a standard Tcl result: TCL_OK means the expression was successfully evaluated, and
TCL_ERROR means that an error occurred while evaluating the expression. If TCL_ERROR is returned then the interpreter's result will hold a
message describing the error. If an error occurs while executing a Tcl command embedded in the expression then that error will be
returned.
If the expression is successfully evaluated, then its value is returned in one of four forms, depending on which procedure is invoked.
Tcl_ExprLong stores an integer value at *longPtr. If the expression's actual value is a floating-point number, then it is truncated to an
integer. If the expression's actual value is a non-numeric string then an error is returned.
Tcl_ExprDouble stores a floating-point value at *doublePtr. If the expression's actual value is an integer, it is converted to floating-
point. If the expression's actual value is a non-numeric string then an error is returned.
Tcl_ExprBoolean stores a 0/1 integer value at *booleanPtr. If the expression's actual value is an integer or floating-point number, then
they store 0 at *booleanPtr if the value was zero and 1 otherwise. If the expression's actual value is a non-numeric string then it must
be one of the values accepted by Tcl_GetBoolean such as "yes" or "no", or else an error occurs.
Tcl_ExprString returns the value of the expression as a string stored in the interpreter's result.
SEE ALSO
Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, Tcl_ExprObj
KEYWORDS
boolean, double, evaluate, expression, integer, object, string
Tcl 7.0 Tcl_ExprLong(3)