在最后20个字节的图像文件中，有一个我需要检索的校验和。我看过Get-Content命令。有没有一种方法可以使读数反向，使其从文件末尾开始？如果不是，是否还有其他命令可用来读取文件的最后20个字节？
答案 0 :(得分：6)
您可以将#!/usr/bin/env python
from subprocess import Popen, PIPE
import time
import sys
import cv2
import os
import csv
import argparse
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
from collections import OrderedDict
from datetime import datetime
PIP_CMD = 'sudo stdbuf -o0 ./pip_sense.v2 l l | stdbuf -o0 grep -P "TX:03(376|004)"'
def run(command):
process = Popen(command, stdout=PIPE, shell=True)
while True:
line = process.stdout.readline().rstrip()
if not line:
break
yield line
print ('Starting...')
def createFolder(directory):
try:
if not os.path.exists(directory):
os.makedirs(directory)
except OSError:
print ('Error: Creating directory. ' + directory)
createFolder('/home/piptag/pip-test/capture_webcam/EXPERIMENTS')
file1 = open('/home/piptag/pip-test/capture_webcam/EXPERIMENTS/3376.txt','w')
file1.write("Time Stamp \t TX ID \t RSSI \tSEQ NO \tCAP \tX-Axis \tY-Axis \tZ-Axis \t X \t Y \t Z \n") # Header line
file1.write("-------------------------------------------------------------------------------------------------------------------------------------\n")
file2 = open('/home/piptag/pip-test/capture_webcam/EXPERIMENTS/3004.txt','w')
file2.write("Time Stamp \t TX ID \t RSSI \tSEQ NO \tX-Axis \tY-Axis \tZ-Axis \t X \t Y \t Z \n") # Header line
file2.write("-------------------------------------------------------------------------------------------------------------------------------------\n")
dirname = "/home/piptag/pip-test/capture_webcam/EXPERIMENTS/"
def save_webcam(dirname):
cam = cv2.VideoCapture(-1) # was getting error (V4L: can't open camera by index 0), thus changes it to -1
jpg_quality = 75
frame_number = 0
if cam.isOpened():
ret_val, img = cam.read()
else:
ret_val = False
timestamp = int(TS)
path = dirname + str(tx) + str("-") + str(timestamp) + ".jpg"
cv2.imwrite(path, img, [int(cv2.IMWRITE_JPEG_QUALITY), jpg_quality])
frame_number = frame_number + 1
##this is the end of the camera program
def twos_comp(val, bits):
"""compute the 2's compliment of int value val"""
if (val & (1 << (bits - 1))) != 0: # if sign bit is set e.g., 8bit: 128-255
val = val - (1 << bits) # compute negative value
return val # return positive value as is
#########################################MAIN###################################
if __name__ == "__main__":
for line in run(PIP_CMD):
raw_data = line.split('\t')
if len(raw_data) > 1:
TS = raw_data[0][3:]
tx = raw_data[3].split(':')[-1]
rssi = float(raw_data[4][5:])
crc_ok = True if (raw_data[5] != b'BAD CRC') else False
no_drop = True if (raw_data[1] == b'Drop:0') else False
# If CRC check is ok and no drop, process the packet
if crc_ok and no_drop:
data = raw_data[-1].split(':')[-1].split()
cat = ""
for i in data:
cat += str(i)
if tx == '03376':
save_webcam(dirname)
print data
CapStatus=data[1]
if CapStatus == '50':
Cap='0'
elif CapStatus == '51':
Cap='1'
SEQNO1=str(int((data[2]),16))
x_axis1=data[3]+data[4]
y_axis1=data[5]+data[6]
z_axis1=data[7]+data[8]
TX1=tx
x1 = twos_comp(int(x_axis1,16), 16) * 0.0039 #* 9.80665 #the value is multiplied by 0.004 as the ADXL345 reports data as 4mg per 1lsb
y1 = twos_comp(int(y_axis1,16), 16) * 0.0039 #* 9.80665 #the value is multiplied by 0.004 as the ADXL345 reports data as 4mg per 1lsb
z1 = twos_comp(int(z_axis1,16), 16) * 0.0039 #* 9.80665 #the value is multiplied by 0.004 as the ADXL345 reports data as 4mg per 1lsb
st1 = str(TS) + "\t "+ "{:<5}".format(str (TX1)) + "\t" + "{:<10}".format(str (rssi)) + "{:<5}".format(SEQNO1) + "\t" + "{:<5}".format(str (Cap)) + "\t" + "{:<5}".format(str (x_axis1)) + "\t" + "{:<5}".format(str (y_axis1)) + "\t"+ "{:<5}".format(str(z_axis1)) + "\t" + "{:<5}".format(str(x1)) + "\t" + "{:<5}".format(str(y1)) + "\t" + "{:<5}".format(str(z1)) +"\n"
file1.write(st1)
elif tx == '03004':
save_webcam(dirname)
print data
SEQNO2=str(int((data[1]),16))
x_axis2=data[2]+data[3]
y_axis2=data[4]+data[5]
z_axis2=data[6]+data[7]
TX2=tx
x2 = twos_comp(int(x_axis2,16), 16) * 0.0039 #* 9.80665 #the value is multiplied by 0.004 as the ADXL345 reports dataas 4mg per 1lsb
y2 = twos_comp(int(y_axis2,16), 16) * 0.0039 #* 9.80665 #the value is multiplied by 0.004 as the ADXL345 reports data as 4mg per 1lsb
z2 = twos_comp(int(z_axis2,16), 16) * 0.0039 #* 9.80665 #the value is multiplied by 0.004 as the ADXL345 reports data as 4mg per 1lsb
st2 = str(TS) + "\t "+ "{:<5}".format(str (TX2)) +"\t "+ "{:<10}".format(str (rssi)) + "{:<5}".format(SEQNO2) + "\t" + "{:<5}".format(str (x_axis2)) + "\t"+ "{:<5}".format(str (y_axis2)) + "\t"+ "{:<5}".format(str(z_axis2))+ "\t"+"{:<5}".format(str(x2)) + "\t" + "{:<5}".format(str(y2))+ "\t"+ "{:<5}".format(str(z2)) +"\n"
file2.write(st2)
file1.close()
file2.close()
的{{1}}参数与Get-Command参数的-Tail值结合使用：
Byte与文档相反，-Encoding并不总是作用于行上。