posix - w3toppers.com

How can I catch a ctrl-c event?

signal isn’t the most reliable way as it differs in implementations. I would recommend using sigaction. Tom’s code would now look like this : #include <signal.h> #include <stdlib.h> #include <stdio.h> #include <unistd.h> void my_handler(int s){ printf(“Caught signal %d\n”,s); exit(1); } int main(int argc,char** argv) { struct sigaction sigIntHandler; sigIntHandler.sa_handler = my_handler; sigemptyset(&sigIntHandler.sa_mask); sigIntHandler.sa_flags = 0; … Read more

Is an atomic file rename (with overwrite) possible on Windows?

See ReplaceFile() in Win32 (http://research.microsoft.com/pubs/64525/tr-2006-45.pdf)

CRON job to run on the last day of the month

Possibly the easiest way is to simply do three separate jobs: 55 23 30 4,6,9,11 * myjob.sh 55 23 31 1,3,5,7,8,10,12 * myjob.sh 55 23 28 2 * myjob.sh That will run on the 28th of February though, even on leap years so, if that’s a problem, you’ll need to find another way. However, it’s … Read more

Atomicity of `write(2)` to a local filesystem

man 2 write on my system sums it up nicely: Note that not all file systems are POSIX conforming. Here is a quote from a recent discussion on the ext4 mailing list: Currently concurrent reads/writes are atomic only wrt individual pages, however are not on the system call. This may cause read() to return data … Read more

How to echo shell commands as they are executed

set -x or set -o xtrace expands variables and prints a little + sign before the line. set -v or set -o verbose does not expand the variables before printing. Use set +x and set +v to turn off the above settings. On the first line of the script, one can put #!/bin/sh -x (or … Read more

How do I check if a directory exists in a Bash shell script?

To check if a directory exists in a shell script, you can use the following: if [ -d “$DIRECTORY” ]; then # Control will enter here if $DIRECTORY exists. fi Or to check if a directory doesn’t exist: if [ ! -d “$DIRECTORY” ]; then # Control will enter here if $DIRECTORY doesn’t exist. fi … Read more

Connecting n commands with pipes in a shell?

Nothing complex here, just have in mind that the last command should output to the original process’ file descriptor 1 and the first should read from original process file descriptor 0. You just spawn the processes in order, carrying along the input side of the previous pipe call. So, here’s are the types: #include <unistd.h> … Read more

What is the equivalent to Posix popen() in the Win32 API?

MSDN explains how you do what popen does using the Windows API in Pipe Handle Inheritance . Here it provides a well-documented example. It’s way more low-level than the _popen function found in the runtime library linked by Jason, but uses the Win32 API exclusively.

Converting year and month (“yyyy-mm” format) to a date?

Since dates correspond to a numeric value and a starting date, you indeed need the day. If you really need your data to be in Date format, you can just fix the day to the first of each month manually by pasting it to the date: month <- “2009-03″ as.Date(paste(month,”-01″,sep=””))

Is file append atomic in UNIX?

A write that’s under the size of ‘PIPE_BUF’ is supposed to be atomic. That should be at least 512 bytes, though it could easily be larger (linux seems to have it set to 4096). This assume that you’re talking all fully POSIX-compliant components. For instance, this isn’t true on NFS. But assuming you write to … Read more