The exec built-in command mirrors functions in the kernel, there are a family of them based on execve, which is usually called from C. exec replaces the current program in the current process, without forking a new process. It is not something you would use in every script you write, but it comes in handy on occasion. Here are some … Read more
I’m assuming you want to still see STDERR and STDOUT on the terminal. You could go for Josh Kelley’s answer, but I find keeping a tail around in the background which outputs your log file very hackish and cludgy. Notice how you need to keep an exra FD and do cleanup afterward by killing it and technically … Read more
What is sh? sh (or the Shell Command Language) is a programming language described by the POSIX standard. It has many implementations (ksh88, Dash, …). Bash can also be considered an implementation of sh (see below). Because sh is a specification, not an implementation, /bin/sh is a symlink (or a hard link) to an actual implementation on most POSIX systems. What is Bash? Bash … Read more
No. From the cron man page: …cron will then examine the modification time on all crontabs and reload those which have changed. Thus cron need not be restarted whenever a crontab file is modified But if you just want to make sure its done anyway, or
I’m looking at functions such as connect() and bind() in C sockets and notice that they take a pointer to a sockaddr struct. I’ve been reading and to make your application AF-Independent, it is useful to use the sockaddr_storage struct pointer and cast it to a sockaddr pointer because of all the extra space it … Read more
This error means you are trying to modify an executable while it is executing. The “Text” here refers to the fact that the file being modified is the text segment for a running program. Use lsof to check what other processes are using it. You can use kill command to kill it if needed.
Using an ls –a and grep, how would you list the name of all of the files in /usr starting with the letter p or the letter r or the letter s using a single grep command? would this be right?
I’m writing a function that perform some authentications actions. I have a file with all the user_id:password:flag couples structured like this: Users.txt user_123:a1b2:0 user_124:a2b1:1 user_125:a2b2:2 This is the code: How can I manage the EOF reaching? I saw that when EOF is reached fgets doesn’t edits anymore the usr_psw_line but neither returns a NULL pointer. … Read more
I am very, very new to UNIX programming (running on MacOSX Mountain Lion via Terminal). I’ve been learning the basics from a bioinformatics and molecular methods course (we’ve had two classes) where we will eventually be using perl and python for data management purposes. Anyway, we have been tasked with writing a shell script to … Read more
S_ISREG() is a macro used to interpret the values in a stat-struct, as returned from the system call stat(). It evaluates to true if the argument(The st_mode member in struct stat) is a regular file. See man stat, man fstat or man inode (link to inode man page) for further details. Here’s the relevant part … Read more