104 lines
2.7 KiB
Bash
104 lines
2.7 KiB
Bash
#! /bin/bash
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#
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# bcalc - a coproc example that uses bc to evaluate floating point expressions
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# If supplied command-line arguments, it uses them as the expression to have
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# bc evaluate, and exits after reading the result. Otherwise, it enters an
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# interactive mode, reading expressions and passing them to bc for evaluation,
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# with line editing and history.
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#
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# You could even use this to write bc programs, but you'd have to rework the
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# single-line REPL a little bit to do that (and get over the annoying timeout
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# on the read)
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#
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# Chet Ramey
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# chet.ramey@case.edu
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# we force stderr to avoid synchronization issues on calculation errors, even
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# with the read timeout
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init()
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{
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coproc BC { bc -q 2>&1; }
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# set scale
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printf "scale = 10\n" >&${BC[1]}
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# bash automatically sets BC_PID to the coproc pid; we store it so we
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# can be sure to use it even after bash reaps the coproc and unsets
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# the variables
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coproc_pid=$BC_PID
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}
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# not strictly necessary; the pipes will be closed when the program exits
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# but we can use it in reset() below
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fini()
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{
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eval exec "${BC[1]}>&- ${BC[0]}<&-"
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}
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reset()
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{
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fini # close the old pipes
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sleep 1
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kill -1 $coproc_pid >/dev/null 2>&1 # make sure the coproc is dead
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unset coproc_pid
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init
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}
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# set a read timeout of a half second to avoid synchronization problems
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calc()
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{
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printf "%s\n" "$1" >&${BC[1]}
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read -t 0.5 ANSWER <&${BC[0]}
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}
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init
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# if we have command line options, process them as a single expression and
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# print the result. we could just run `bc <<<"scale = 10 ; $*"' and be done
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# with it, but we init the coproc before this and run the calculation through
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# the pipes in case we want to do something else with the answer
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if [ $# -gt 0 ] ; then
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calc "$*"
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printf "%s\n" "$ANSWER"
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fini
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exit 0
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fi
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# we don't want to save the history anywhere
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unset HISTFILE
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while read -e -p 'equation: ' EQN
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do
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case "$EQN" in
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'') continue ;;
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exit|quit) break ;;
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reset) reset ; continue ;;
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esac
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# save to the history list
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history -s "$EQN"
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# run it through bc
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calc "$EQN"
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if [ -n "$ANSWER" ] ; then
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printf "%s\n" "$ANSWER"
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fi
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done
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fini
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exit 0
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