C program to monitor and notify changes in a directory / file using inotify

 $ vim notify.c 
[bash] #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <sys/types.h> #include <sys/inotify.h> #include <limits.h> #include <unistd.h> #define MAX_EVENTS 1024 /*Max. number of events to process at one go*/ #define LEN_NAME 1024 /*Assuming length of the filename won’t exceed 16 bytes*/ #define EVENT_SIZE ( sizeof (struct inotify_event) ) /*size of one event*/ #define BUF_LEN ( MAX_EVENTS * ( EVENT_SIZE + LEN_NAME )) /*buffer to store the data of events*/ void get_event (int fd) { char buffer[BUF_LEN]; int length, i = 0; length = read( fd, buffer, BUF_LEN ); if ( length < 0 ) { perror( "read" ); } while ( i < length ) { struct inotify_event *event = ( struct inotify_event * ) &buffer[ i ]; if ( event->len ) { if ( event->mask & IN_CREATE) { if (event->mask & IN_ISDIR) printf( "The directory %s was Created.\n", event->name ); else printf( "The file %s was Created with WD %d\n", event->name, event->wd ); } if ( event->mask & IN_MODIFY) { if (event->mask & IN_ISDIR) printf( "The directory %s was modified.\n", event->name ); else printf( "The file %s was modified with WD %d\n", event->name, event->wd ); } if ( event->mask & IN_DELETE) { if (event->mask & IN_ISDIR) printf( "The directory %s was deleted.\n", event->name ); else printf( "The file %s was deleted with WD %d\n", event->name, event->wd ); } i += EVENT_SIZE + event->len; } } } int main( int argc, char **argv ) { int wd, fd; fd = inotify_init(); if ( fd < 0 ) { perror( "Couldn’t initialize inotify"); } wd = inotify_add_watch(fd, argv[1], IN_CREATE | IN_MODIFY | IN_DELETE); if (wd == -1) { printf("Couldn’t add watch to %s\n",argv[1]); } else { printf("Watching:: %s\n",argv[1]); } /* do it forever*/ while(1) { get_event(fd); } /* Clean up*/ inotify_rm_watch( fd, wd ); close( fd ); return 0; } [/bash]
 $ gcc -o notify notify.c 

Now open another terminal and lets create a test directory as,

 $ mkdir helloworld_dir 

In the previous terminal, start notify program as,

 $ ./notify helloworld_dir/
Watching:: helloworld_dir/ 

Now, go to another terminal and create a test file,

 $ cd helloworld_dir 

$ touch hello.txt

In this case, the first terminal will print like below,

$ ./notify helloworld_dir/
Watching:: helloworld_dir/
The file hello.txt was Created with WD 1

Now, in another window try to edit the hello.txt as,

 $ echo "modify hello.txt to add some lines " > hello.txt 

Then the first terminal should print a message as,

 The file hello.txt was modified with WD 1 

Reference : https://opensourceforu.com/2011/04/getting-started-with-inotify/

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