Command line wrapper for dc (1)
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README.md

NAME

wrapdc - Command line wrapper for dc (1)

SYNTAX

wrapdc [-v] [pseudocommand] [command]

DESCRIPTION

This wrapper renders dc more usable as a command line calculator by:

  • defining commonly used macros for more complex operations
  • saving precision, top of stack, and registers 0 to 9 ("memories") from one invocation to the next in the status file $HOME/.wdcrc
  • saving last top of stack value in ${TMPDIR:-/tmp}/wdc-$USER for further direct use (change file name in the source, if desired)

PREREQUISITES

The POSIX conform program dc ("desktop calculator") and standard shell sh must be installed and accessible through $PATH.

USAGE

The wrapper script wrapdc.sh can be called directly (if executable) or by invoking sh wrapdc.sh with optional arguments.

If arguments are given, they are interpreted as one line of commands, which is executed, and then the script finishes.

If no arguments are given, the script enters a loop: read a line of input from STDIN, execute it, and display the resulting top-of-stack, together with the top of stack in exponential notation (which currently only works as usual for absolute values greater than 1). The loop (and script) finishes, when quit or CTRL-D is entered.

All normal dc commands can be used, see the corresponding manual. In particular, negative numbers must be entered with a leading _ (underscore) as minus sign, not a - (dash), because the latter is indicating the command 'subtraction'.

As an extension, values can also be entered in exponential notation, e.g 12e3 is converted to 1200 and 1E_2 to .01 (if precision is 2).

The dc command r (exchanging the two topmost stack entries) is emulated with some internal register operations, as it is a GNU extension and may not always be available. This may render complex operations somewhat slower.

There is also a macro drop for removing the topmost stack value.

In addition to the quit command, the following pseudocommands are handled directly by the wrapper:

  • help shows some initial hints and this pseudocommand list
  • list displays a list of predefined macros; please note the syntax is according to sed i.e certain characters are escaped with backslash
  • verb activates verbose mode, which displays before each execution of input line the input from the status file as well as the input line with expanded macro definitions
  • noverb deactivates verbose mode
  • clear resets precision and all memories and stack registers

All pseudocommands must be entered at the beginning of a line, and all subsequent input on this line will be ignored.

Verbose mode can also be activated with the command line option -v which may be useful in case of direct input with further command line arguments.

Statistical Calculations

The registers ("memories") 1 to 6 have special meanings for statistical calculations with $... macros, and are used as follows:

  • reg.1 = number of entries n
  • reg.2 = sum of X values sumX
  • reg.3 = sum of X^2 values sumX2
  • reg.4 = sum of Y values sumY
  • reg.5 = sum of Y^2 values sumY2
  • reg.6 = sum of XY values sumXY

The command $ or $+ adds the two topmost stack values to the statistical registers as follows: the topmost value is added to reg.2 and its square value to reg.3, the second to topmost value in the same way to reg.4 and 5, and the product of the two values to reg.6. reg.1 is then increased by 1.

The command $- subtracts the values in the inverse way. Please note: due to rounding errors, $- is not the inverse of $+ in some cases.

The command $m calculates the mean values reg.2/reg.1 and reg.4/reg.1.

(More commands will be added in future versions.)

EXAMPLES

(We assume wrapdc.sh is executable in $PATH .)

$ wrapdc.sh 5k 2v # precision 5, 2 on stack, calculate square root
1.41421 # 1.41421E0
$ wrapdc.sh 3 7/ # 3, divide by 7 (precision was saved from last run)
.42857 # 4.28570E-1
$ wrapdc.sh list # display macros (and top of stack before finishing)
: %t # percent part: X:=100*X/Y, Y kept
: %d # percent delta: X:=100*(X-Y)/Y, Y kept
: % # percentage: X:=X*Y/100, Y kept
: rem # remainder: X:=Y%X (instead of normal % command)
: sto\(.\) # sto.: store with copying (i.e keep value on stack)
: fact # factorial: X:=X!
: neg # negate: X:=-X
: \$m # mean value: X:=reg.2/reg.1, Y:=reg.4/reg.1
: \$- # remove statistic entry
: \$+* # add statistic entry
: [eE]\(_*[0-9][0-9]*\) # infix exponential: X:=X*10^N
: drop # stack drop
: r # revert: X:=Y, Y:=X (r is a GNU extension)
.42857 # 4.28570E-1
$ wrapdc.sh 42fact sto1 # calculate 42! (factorial) and store in '1'
1405006117752879898543142606244511569936384000000000 # 1.40500E51
$ wrapdc.sh 2k234 7%+ # precision 2, add 7% to 234
250.38 # 2.50E2
$ wrapdc.sh 234r%t # which is how many % of 234?
107.00 # 1.07E2
$ wrapdc.sh l1 40fact/ # divide memory '1' by the factorial of 40
1722.00 # 1.72E3
$ wrapdc.sh 41 42* # which of course is 42!/40!=41*42
1722 # 1.72E3
$ wrapdc.sh clear # set all registers to 0 (prepare for statistics)
0 # 0E-1
$ wrapdc.sh '1$2$3$4$l2' # entries: 1,2,3,4; load reg.2 (sum)
10 # 1.00E1
$ wrapdc.sh '$m' # display average of statistic entries
2.50 # 2.50E0
$ wrapdc.sh 1234fact|sed -e 's/.*#//' # 1234!, only display exponential
 5.10E3280
$ wrapdc.sh 1233fact/ # just checking: 1234!/1233!=1234
1234.00 # 1.23E3
$ wrapdc.sh 1.23e3- # just checking exponential notation
4.00 # 4.00E0

Note: the example with 41 42* only works if there is no file beginning with '42' in the current directory, otherwise the shell will expand its name before passing on the argument to the wrapper script. In this case, you should escape the * or put the arguments in apostrophes '41 42*' or simply start the wrapper without arguments, and do the calculations in its internal command loop. Preventing shell expansion is also necessary in the statistics example.

MACROS

Macros can be easily added to the script, if you know sed syntax. They are defined in the shell variable mcrs. where each one should be written on a separate line with comma , as pattern delimiters, followed by ;# and a comment explaining its use. This allows the list pseudocommand to display them together with the comment. Do not prepend any white space to the definition, otherwise it will not be displayed by list!

Please note that the macro expansion is global and "stupid" -- you should therefore define the longer commands first, and single character commands only at the very end. Otherwise, e.g the rem command would first have its r expanded as the "revert" command, therefore rem expansion would fail.

FILES

  • The status between invocations is stored in the file $HOME/.wdcrc as a list of dc commands.
  • The last top of stack value is stored in /tmp/wdc-$USER.

These file names can be easily changed at the beginning of the script.

BUGS

(certainly, but none known at this moment)


AUTHOR

Yargo Bonetti