Generic dichotomic search as a shell script

dichotomic-bash.sh

#!/usr/bin/env bash
# Dichotomic search in bash
# This is a bash-specific function that uses bash features.
# This is not guaranteed to work in other shells.
#
# Usage:
#     source dichotomic-bash.sh
#     result=$(dichotomic_search min max command)
#
# Returns the largest i for which `command i` succeeds (exits with a null exit code)
# This supposes that there is an i such that :
#     forall min <= n <= i, `command n` succeeds,
# and forall i < n <= max, `command n` fails
#
# This script is public domain

function dichotomic_search {
  min=$1
  max=$2
  command=$3

  while (( $min < $max )); do
    # Compute the mean between min and max, rounded up to the superior unit
    current=$(( (min + max + 1 ) / 2 ))
    if $command $current
      then min=$current
      else max=$((current - 1))
    fi
  done

  echo $min
}

dichotomic.sh

#!/bin/sh
# Dichotomic search in shell
# Usage: dichotomic.sh min max command
# Returns the largest i for which `command i` succeeds (exits with a null exit code)
# This supposes that there is an i such that :
#     forall min <= n <= i, `command n` succeeds,
# and forall i < n <= max, `command n` fails
# This script works in any shell (not just bash) and is public domain

if [ "$#" -ne 3 ]; then
  echo "$0: invalid number of parameters.
  Usage: $0 min max command" >&2
  exit 1
fi

min=$1
max=$2
command=$3

while [ $min -lt $max ]; do
  # Compute the mean between min and max, rounded up to the superior unit
  current=`expr '(' "$min" + "$max" + 1 ')' / 2`
  if $command $current
    then min=$current
    else max=`expr $current - 1`
  fi
done

echo $min

Yo this is super sexy. thanks

Thank you very much for the script, but [[ $min < $max ]] will not work correctly in bash, it should be changed to [[ $min -lt $max ]] just like in the POSIX version (Changing [ to [[ doesn't magically change < from string comparison to integer comparison). Or use (( $min < $max )) instead.

@William8915 : you are right, thanks ! I changed it