GEXPR(1)GEXPR(1)NAMEgexpr - handy shell calculator
SYNOPSISgexpr [ options ] expression
DESCRIPTIONgexpr is an expression parser that can be used as a simple command-line
calculator, as in gexpr 'sin(pi/4)*sqrt(4)', or to add floating point
math to shell scripts. It is meant to be an alternative to bc (1),
being less powerful but lighter and much more intuitive. It also pro‐
vides a few nice features of its own.
If an expression is given as argument, it must be protected from the
shell using quotes as in the example above. If you fail to do so,
parentheses will be interpreted and the * character will be expanded by
the shell, wreaking havoc. Using double quotes " " is necessary if you
want to use shell variables within expression.
gexpr supports the usual arithmetical operators + - * / , the rela‐
tional operators < <= > >= == != , and all the standard C mathematical
functions apart from frexp (3) and modf (3), which cannot be fully
implemented since they actually return two values. In addition, gexpr
provides the constants defined in math.h (M_PI, etc), the fact(n) func‐
tion, which returns the factorial of n, and the rnd(n) function, which
returns a random number between 0 and n.
A nice feature of gexpr is the possibility of using other bases than
10. For instance, this expression is allowed:
$ gexpr "0x10 + 0b1010 + 010"
34
$ _
the prefix "0x" denotes numbers written in base 16, "0b" numbers in
base 2, and "0" octal numbers.
The command "base nn" is used to display the results in a base between
2 and 16. Example:
gexpr> base 16
output base is now 16
gexpr> 256 * 2
200
gexpr> _
The command "decimals nn" (or "dec nn") specifies the number of decimal
positions. Example:
gexpr> PI
3.1415926525
gexpr> dec 20
decimal positions now 20
gexpr> PI
3.14159265258979311740
gexpr> _
COMMANDS
base specify the output base.
dec(imals)
specify the number of decimals (default: 10).
help display a list of functions, constants, and commands.
q(uit) quit the program.
OPTIONS--help, -h
display a short help.
--base n, -b n
output results in base n.
--no_prompt, -n
don't display the gexpr> prompt.
EXAMPLESgexpr 2 + 10 / 2
gexpr "sqrt(5) < log(10)"
echo "sqrt(2)/2" | gexpr-n
gexpr "sin($X) - tan($Y)"
gexpr "$X + ($Y)*log10(${ZZ})"
This is an interesting use of gexpr in a shell script:
#!/bin/sh DEC=`echo "M_PI_2" | gexpr -n` EXA=`echo "M_PI_2" | gexpr-n
-b16` echo "Pi/2 is $DEC (or $EXA in hexa)"
Another example:
#!/bin/sh
X=0
while [ `gexpr "$X < 10"` = 1 ]
do
X=`gexpr "$X + 0.2"`
echo $X
done
BUGS
It is awfully slow and its use cannot replace a "real" programming lan‐
guage supporting floating point math.
Most errors are trapped but some are not, like overflows and under‐
flows. For example, on the Linux box it was written on gexpr overflows
when the result exceeds about 1.797e+308.
It would be nice to add command-line editing. This would make gexpr
quite bigger, though.
AUTHOR
Guido Gonzato <ggonza@tin.it>
SEE ALSO
expr (1), sh (1), bc (1)
GEXPR 2.0.2 May 2001 GEXPR(1)
