Controlling bash Features and Options

This section explains how to controlbash features and options using command line options and the set andshopt builtins.

Command Line Options

Two kinds of command line options are available: short and long. Short options consist of a hyphen followed by a letter; long options have two hyphens followed by multiple characters. Long options must appear before short options on a command line that calls bash. Table 8-12 lists some commonly used command line options.

Table 8-12. Command line options

Option

Explanation

Syntax

Help

Displays a usage message.

--help

No edit

Prevents users from using the Readline Library (page 304) to edit command lines in an interactive shell.

--noediting

No profile

Prevents reading these startup files (page 259): /etc/profile, ~/.bash_profile, ~/.bash_login, and ~/.profile.

--noprofile

No rc

Prevents reading the ~/.bashrc startup file (page 260). This option is on by default if the shell is called as sh.

--norc

POSIX

Runs bash in POSIX mode.

--posix

Version

Displays bash version information and exits.

--version

Login

Causes bash to run as though it were a login shell.

--I (lowercase "I")

shopt

Runs a shell with the opt shopt option (page 318). A -0 (uppercase "0") sets the option; +0 unsets it.

[±]0 [ opt ]

End of options

On the command line, signals the end of options. Subsequent tokens are treated as arguments even if they begin with a hyphen (-).

Shell Features

You can control the behavior of the Bourne Again Shell by turning features on and off. Different features use different methods to turn features on and off. The set builtin controls one group of features, while the shopt builtin controls another group. You can also control many features from the command line you use to call bash.

set ±o: Turns Shell Features On and Off

The set builtin (there is a set builtin in tcsh, but it works differently), when used with the -o or +ooption, enables, disables, and lists certain bash features. For example, the following command turns on the noclobber feature (page 125):

   $ set -o noclobber

You can turn this feature off (the default) by giving the command

   $ set +o noclobber

The command set -o without an option lists each of the features controlled by set followed by its state (on or off). The command set +o without an option lists the same features in a form that you can use as input to the shell. Table 8-13 lists bash features.

Table 8-13. bash features

Feature

Description

Syntax

Alternate syntax

allexport

Automatically exports all variables and functions that you create or modify after giving this command.

set –o allexport

set –a

braceexpand

Causes bash to perform brace expansion (the default; page 323).

set –o braceexpand

set –B

cdspell

Corrects minor spelling errors in directory names used as arguments to cd.

shopt –s cdspell

 

cmdhist

Saves all lines of a multiline command in the same history entry, adding semicolons as needed.

shopt –s cmdhist

 

dotglob

Causes shell special characters (wildcards; page 133) in an ambiguous file reference to match a leading period in a filename. By default special characters do not to match a leading period. You must always specify the filenames . and ..explicitly because no pattern ever matches them.

shopt –s dotglob

 

emacs

Specifies emacs editing mode for command line editing (the default; page 305).

set –o emacs

 

errexit

Causes bash to exit when a simple command (not a control structure) fails.

set –o errexit

set –e

execfail

Causes a shell script to continue running when it cannot find the file that is given as an argument to exec. By default a script terminates whenexec cannot find the file that is given as its argument.

shopt –s execfail

 

expand_aliases

Causes aliases (page 311) to be expanded (by default it is on for interactive shells and off for noninteractive shells).

shopt –s expand_alias

 

hashall

Causes bash to remember where commands it has found using PATH (page 285) are located (default).

set –o hashall

set –h

histappend

Causes bash to append the history list to the file named by HISTFILE (page 295) when the shell exits. By default bash overwrites this file.

shopt –s histappend

 

histexpand

Causes the history mechanism (which uses exclamation points; page 299) to work (default). Turn this feature off to turn off history expansion.

set –o histexpand

set –H

history

Enable command history (on by default; page 295).

set –o history

 

ignoreeof

Specifies that bash must receive ten EOF characters before it exits. Useful on noisy dial-up lines.

set –o ignoreeof

 

monitor

Enables job control (on by default, page 272).

set –o monitor

set –m

nocaseglob

Causes ambiguous file references (page 133) to match filenames without regard to case (off by default).

shopt –s nocaseglob

 

noclobber

Helps prevent overwriting files (off by default; page 125).

set –o noclobber

set –C

noglob

Disables pathname expansion (off by default; page 133).

set –o noglob

set –f

notify

With job control (page 272) enabled, reports the termination status of background jobs immediately. The default behavior is to display the status just before the next prompt.

set –o notify

set –b

nounset

Displays an error and exits from a shell script when you use an unset variable in an interactive shell. The default is to display a null value for an unset variable.

set –o nounset

set –u

nullglob

Causes bash to expand ambiguous file references (page 133) that do not match a filename to a null string. By default bash passes these file references without expanding them.

shopt –s nullglob

 

posix

Runs bash in POSIX mode.

set –o posix

 

verbose

Displays command lines as bash reads them.

set –o verbose

set –v

vi

Specifies vi editing mode for command line editing (page 304).

set –o vi

 

xpg_echo

Causes the echo builtin to expand back-slash escape sequences without the need for the –eoption (page 548).

shopt –s xpg_echo

xtrace

Turns on shell debugging (page 536).

set –o xtrace

set –x

shopt: Turns Shell Features On and Off

The shopt (shell option) builtin (not available in tcsh) enables, disables, and lists certain bashfeatures that control the behavior of the shell. For example, the following command causes bashto include filenames that begin with a period (.) when it expands ambiguous file references (the -sstands for set):

   $ shopt -s dotglob

You can turn this feature off (the default) by giving the command (the –u stands for unset)

$ shopt -u dotglob

The shell displays how a feature is set if you give the name of the feature as the only argument toshopt:

$ shopt dotglob
dotglob           off

The command shopt without any options or arguments lists the features controlled by shopt and their state. The command shopt -s without an argument lists the features controlled by shopt that are set or on. The command shopt –u lists the features that are unset or off. Table 8-13 lists bashfeatures.

<think>好的,我现在需要帮助用户解决如何用C++控制海康威视工业相机和伺服电机的问题。首先,我得确定用户的具体需求是什么。他们可能是在做自动化项目,需要同时控制相机和电机,比如在视觉引导的机械臂系统中,相机捕捉位置,然后电机调整位置。 接下来,我需要考虑海康威视相机的控制方式。根据之前的引用,海康威视的相机通常使用ONVIF协议或SDK。用户可能需要通过SDK来获取图像或控制相机参数。而伺服电机通常通过Modbus、EtherCAT或者特定的控制器指令来控制,比如使用RS485通信。 然后,我得回忆是否有相关的C++示例代码。海康威视的官网或开发者平台可能会有SDK和示例,用户可能需要先下载SDK,并按照文档配置环境。对于伺服电机,可能需要第三方库或者厂商提供的API,比如Modbus的库如libmodbus。 接下来,我需要组织一个基本的示例结构。可能需要分开相机控制和电机控制两部分。相机部分可能包括初始化、捕获图像、释放资源;电机部分包括连接、移动、断开。同时,需要处理错误情况,比如连接失败或指令执行错误。 需要注意的是,用户可能需要具体的SDK函数和电机协议细节,但如果没有具体型号和文档,代码只能是框架性的。因此,在回答中应该建议用户查阅官方文档,并确保包含必要的头文件和链接库。 另外,用户可能遇到的问题包括环境配置、SDK版本兼容性、通信协议的选择等。可能需要提醒用户注意这些方面,并提供获取帮助的途径,如官方支持或社区论坛。 最后,生成相关问题,帮助用户深入解决可能遇到的后续问题,比如性能优化、多线程处理、错误处理等。</think>[用户可见层] # 海康威视工业设备控制C++代码框架 ## 一、工业相机控制基础 海康威视工业相机需通过官方SDK进行控制,开发流程包含: 1. 下载MVS开发套件(含Windows/Linux版) 2. 配置开发环境(需安装OpenCV等视觉库) 3. 使用SDK中的设备发现、图像采集API 示例代码框架: ```cpp #include "MvCameraControl.h" void CameraControl() { MV_CC_DEVICE_INFO_LIST stDeviceList; MV_CC_EnumDevices(MV_GIGE_DEVICE | MV_USB_DEVICE, &stDeviceList); // 创建相机实例 void* handle = nullptr; MV_CC_CreateHandle(&handle, stDeviceList.pDeviceInfo[0]); // 连接设备 MV_CC_OpenDevice(handle); // 设置触发模式(示例为连续采集模式) MV_CC_SetEnumValue(handle, "TriggerMode", MV_TRIGGER_MODE_OFF); // 开始采集 MV_CC_StartGrabbing(handle); // 获取图像数据 MV_FRAME_OUT stImageInfo; MV_CC_GetImageBuffer(handle, &stImageInfo, 1000); // 处理图像... // 释放资源 MV_CC_StopGrabbing(handle); MV_CC_CloseDevice(handle); MV_CC_DestroyHandle(handle); } ``` ## 二、伺服电机控制基础 常见伺服控制方式(以Modbus-RTU为例): ```cpp #include <modbus.h> void ServoControl() { modbus_t* ctx = modbus_new_rtu("/dev/ttyUSB0", 9600, 'N', 8, 1); modbus_set_slave(ctx, 1); // 设置从站地址 if(modbus_connect(ctx) == -1) { std::cerr << "Connection failed: " << modbus_strerror(errno); return; } // 写入目标位置(示例地址40001) uint16_t target_position = 1000; modbus_write_register(ctx, 0, target_position); // 读取当前位置 uint16_t current_pos; modbus_read_registers(ctx, 1, 1, &current_pos); modbus_close(ctx); modbus_free(ctx); } ``` ## 三、系统集成建议 1. 线程管理:建议使用独立线程处理图像采集和电机控制 2. 同步机制:通过共享内存/队列实现视觉坐标到电机位置的转换 3. 错误处理:增加超时重试和异常中断机制
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值