find-first-fail: renamed from binsearch.
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Ole Tange
parent
b29b851281
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214
find-first-fail/find-first-fail
Executable file
214
find-first-fail/find-first-fail
Executable file
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@ -0,0 +1,214 @@
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#!/bin/bash
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: <<'=cut'
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=encoding utf8
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=head1 NAME
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find-first-fail - find the lowest argument that makes a command fail
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=head1 SYNOPSIS
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B<find-first-fail> [-2] [-q] I<command>
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=head1 DESCRIPTION
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B<find-first-fail> runs I<command> with a single number. It returns highest
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value that I<command> succeeds for.
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It finds the value by first testing the value 1. As long as the value
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succeeds, the value is doubled. When the value fails, B<find-first-fail>
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does a binary search between this value and the previous value.
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If the value 1 fails, B<find-first-fail> instead searches for the highest
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value that I<command> fails for.
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=head1 OPTIONS
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=over 4
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=item B<-2>
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Instead of passing the command a single argument, give the command 2
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arguments: I<from> I<to>.
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=item B<-q>
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Quiet. Ignore output from I<command>.
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=back
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=head1 EXAMPLES
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=head2 Find the last file
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This is a silly way to find the last non-existing file (namely 244):
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touch {245..800}
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find-first-fail ls
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This is a silly way to find the last file (namely 800):
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touch {1..800}
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find-first-fail ls
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=head2 Test a bash function
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Test how long an argument /bin/echo can take
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. $(which find-first-fail)
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singleecho() {
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/bin/echo $(perl -e 'print "x"x'$1) >/dev/null
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}
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find-first-fail singleecho
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=head2 Test a bash function that takes from and to as arguments
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Use a function that takes two arguments. It finds the line number
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after HOME=.
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. $(which find-first-fail)
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greplines() {
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env | perl -ne "$1..$2 and print" | grep HOME=
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}
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find-first-fail -2 -q greplines
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=head2 Test complex command and show what is run
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Complex commands can also be run:
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find-first-fail -v perl -e 'exit(shift > 129)'
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=head1 AUTHOR
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Copyright (C) 2020 Ole Tange,
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http://ole.tange.dk and Free Software Foundation, Inc.
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=head1 LICENSE
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Copyright (C) 2012 Free Software Foundation, Inc.
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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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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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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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=head1 SEE ALSO
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B<eval>(1)
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=cut
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find-first-fail() {
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_find-first-fail() {
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low=$1
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high=$2
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# echo $low-$high
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if [ $low -gt $(($high - 2)) ]; then
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return
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fi
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shift
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shift
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middle=$(( ( $low + $high ) / 2 ))
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if _run $low $middle "$@" ; then
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low=$middle
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else
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high=$middle
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fi
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_find-first-fail $low $high "$@"
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}
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_run() {
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# run:
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# cmd $low $high
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# or:
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# cmd $value
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# Output is ignored if $quiet
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# Exit value is negated if $not
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_inner_run() {
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# _inner_run is needed if cmd is complex like:
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# perl -e 'exit( (shift) + (shift) > 10)'
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if $opt2 ; then
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$verbose && echo "${cmd[@]}" "$a" "$b"
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"${cmd[@]}" "$a" "$b"
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else
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$verbose && echo "${cmd[@]}" "$b"
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"${cmd[@]}" "$b"
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fi
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}
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local a="$1"
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local b="$2"
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shift
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shift
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# echo "a=$a b=$b $@"
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local cmd=( "$@" )
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eval "$not" _inner_run "$quiet"
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}
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quiet=""
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opt2=false
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verbose=false
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# Parse and remove options
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while getopts "2vq" options; do
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case "${options}" in
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(2) opt2=true;;
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(q) quiet=">/dev/null 2>/dev/null";;
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(v) verbose=true;;
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(-) break;;
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esac
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done
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shift $(( OPTIND - 1))
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# If function(1) = false: run 'not function()' instead
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if _run 1 1 "$@" ; then
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not=''
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else
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not='!'
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fi
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# exponential search for the first value that is false
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# low = previous value (function($low) == true)
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# high = low * 2 (function($high) == false)
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high=1
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while _run 1 $high "$@" ; do
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low=$high
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high=$(( $high*2 ))
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if [ $high -gt 4611686018427387900 ] ; then
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echo "$0: Error: exit value does not change of '$@'" >&2
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return
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fi
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done
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# low = tested good
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# high = tested fail
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# Search low..high
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# echo "low: $low high: $high not: $not"
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_find-first-fail $low $high "$@" 2>/dev/null
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echo $low
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}
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if [ -z "$*" ] ; then
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# source the bash function
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# . $(which find-first-fail)
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true
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else
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# find-first-fail command
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find-first-fail "$@"
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fi
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