unix

问题 A process has a 'fork' call after a signal handler has been registered [for SIGINT]. what happens when SIGINT is sent through command line ? whether parent gets exited or child or both ? parent and child both are running infinite while loops. 回答1: If you do fork (without further exec* ) after a signal handler has been registered, the same signal handler will be used in parent and child processes. That is, if you do something other than exit in your SIGINT handler, neither parent nor child

问题 I'm writing a pretty basic application in python (it's only one file at the moment). My question is how do I get it so the python script is able to be run in /usr/bin without the .py extension? For example, instead of running python htswap.py args from the directory where it currently is, I want to be able to cd to any directory and do htswap args Thanks in advance! 回答1: Simply strip off the .py extension by renaming the file. Then, you have to put the following line at the top of your file:

问题 I am trying to figure out the performance of my code, but I do not understand the output of the time command, Can anybody please explain what does time command output means. The following is what I get: time ./filereader real 0m0.193s user 0m0.012s sys 0m0.056s What is real , user , sys ? 回答1: From: http://zch051383471952.blogspot.com/2010/01/different-of-real-user-sys-time.html Real refers to actual elapsed time; User and Sys refer to CPU time used only by the process. Real is wall clock

问题 I am trying to figure out the performance of my code, but I do not understand the output of the time command, Can anybody please explain what does time command output means. The following is what I get: time ./filereader real 0m0.193s user 0m0.012s sys 0m0.056s What is real , user , sys ? 回答1: From: http://zch051383471952.blogspot.com/2010/01/different-of-real-user-sys-time.html Real refers to actual elapsed time; User and Sys refer to CPU time used only by the process. Real is wall clock

问题 I wish to know which of these two options is the more secure one to use: #define MAXLEN 255 char buff[MAXLEN + 1] sprintf(buff, "%.*s", MAXLEN, name) snprintf(buff, MAXLEN, "%s", name) My understanding is that both are same. Please suggest. 回答1: The two expressions you gave are not equivalent: sprintf takes no argument specifying the maximum number of bytes to write; it simply takes a destination buffer, a format string, and a bunch of arguments. Therefore, it may write more bytes than your

问题 I wish to know which of these two options is the more secure one to use: #define MAXLEN 255 char buff[MAXLEN + 1] sprintf(buff, "%.*s", MAXLEN, name) snprintf(buff, MAXLEN, "%s", name) My understanding is that both are same. Please suggest. 回答1: The two expressions you gave are not equivalent: sprintf takes no argument specifying the maximum number of bytes to write; it simply takes a destination buffer, a format string, and a bunch of arguments. Therefore, it may write more bytes than your

问题 I'm trying to interpret this block of code. Searched google to see what these commands mean and no luck. I put my interpretation of what each line/block means to me. If I am wrong, please correct me. I am new to unix commands. Code: #!/bin/bash # input 1st command line argument for the version. export VERSION=$1 # if user didn't input a version, print the echo message and exit (not sure what -n means but I am assuming) if [[ ! -n "$VERSION" ]]; then echo "Missing Version" exit 1 fi # creating

问题 I have the following scenario: Rasperry pi connected to a device via Serial port 3g Dongle connected to the raspberry (with the ability to make/recieve calls) One process reading the data from the serial port and redirecting it to a server (using 3g) Another process waiting for a incoming call, and when someone calls the program takes the data from the serial port and redirect it via the 3g dongle using AT commands ( like fax-call). When someone calls, the call is made using AT commands and

问题 I'm trying to create a very simple bash script that does the following: Inputs the user to enter a project folder Sets the value entered in a variable cd to the folder entered remove the readme.md file From what I've read around I've come up with this: #!/bin/bash echo "Enter the project folder path:" read -e DESTINATION_FOLDER cd "$DESTINATION_FOLDER" rm -rf "$DESTINATION_FOLDER/readme.md" The folder's path I entered was ~/Dropbox/myproject And the error I get is the one below. However that

问题 I am writing a script and which requires to calculate the difference between the two timestamps . I have done some search but didn't get a clue so far. For Example say: time1 = 20160314 10:16:27 time2 = 20160313 15:17:28 From the above I need to get result like below: difference is: " 1 day 5 hours 1 minute 1 second " Please help me in resolving this. 回答1: datediff() { t1=$(date -d "$1" +%s) t2=$(date -d "$2" +%s) diff=$(( $t1 - $t2 )) echo "Duration: $(( $diff / 86400 )) days $(($diff / 3600