GEXPR(1) General Commands Manual GEXPR(1) NAME gexpr - handy shell calculator SYNOPSIS gexpr [ options ] expression DESCRIPTION gexpr 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 provides 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 relational 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) function, which returns the fac- torial 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 po- sitions. 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. EXAMPLES gexpr 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 language supporting floating point math. Most errors are trapped but some are not, like overflows and underflows. 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)
NAME | SYNOPSIS | DESCRIPTION | COMMANDS | OPTIONS | EXAMPLES | BUGS | AUTHOR | SEE ALSO
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