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