bluetoothctl-file

#!/bin/sh
#
# shellcheck shell=dash
#

# Use environment variable otherwise use default
bltctlDevicesFile=${bltctlDevicesFile:-/app/bltctl-devices.out}
bltctlScanFile=${bltctlScanFile:-/app/bltctl-scan.out}

# Function to randomly read X lines starting at a random line:
#   - randomly pick a start line (startLine)
#   - randomly pick number of line to read between
fileRandomRead() {
  fileName=$1 # file to read
  nPickMin=$2 # min number of lines to pick
  nPickMax=$3 # max number of lines to pick

  # Read from file
  [ ! -f $fileName ] &&
    log_fatal "Error bluetoothctl-file input file $fileName not found" &&
    exit 30

  # Number of lines in fileName
  finputTotalLines=$(wc -l <"$fileName")
  # nPick to be within the file line count and the nPickMax
  nPick=$((RANDOM % ((finputTotalLines < nPickMax ? \
    finputTotalLines : nPickMax) - nPickMin + 1) + nPickMin))
  # Pick a startLine
  startLine=$((RANDOM % (finputTotalLines - nPick + 1) + 1)) # Random starting line

  # Extract nPick lines starting from line startLine
  # sed -u (unbuffered) requires GNU sed
  sed -u -n "${startLine},$((startLine + nPick - 1))p" "$fileName"
}

# Loop to process incoming commands
processBltctlCmd() {
  while :; do
    if read -r bltctlCmd; then
      case $bltctlCmd in
      devices)
        fileRandomRead $bltctlDevicesFile 0 10
        ;;
      scan*on)
        fileRandomRead $bltctlScanFile 0 35
        ;;
      esac
    fi
  done
}

trap 'exit 0' INT

processBltctlCmd