Tail -f on new files
Solution 1:
Thanks all for support, but since nor mutitail nor tail -F nor watch tail seems to help for what I need, I developed a small solution in C. I post the code here, since maybe someone can find it useful. (There are missing checks and some weakness I know, but so far it's enough)
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/inotify.h>
#include <sys/stat.h>
#include <signal.h>
#include <dirent.h>
#include <linux/limits.h>
#define CHAR_BACK 500
// * File handler structure
struct file_followed { long last_position; char filename[NAME_MAX]; struct file_followed * next; };
struct file_followed * file_list = NULL;
// * To quit peacefully
int cycle = 1;
void stopCycle(int u) { cycle = 0; }
// * Last tailed filename
char last_tailed[NAME_MAX];
void fileAdd(char * file) {
struct file_followed ** list = &file_list;
struct stat statdesc;
if(stat(file, &statdesc) || !S_ISREG(statdesc.st_mode)) { return; }
while(*list) { list = &((*list)->next); }
*list = malloc(sizeof(struct file_followed));
(*list)->last_position = -1;
strcpy((*list)->filename, file);
(*list)->next = NULL;
}
int fileTail(struct file_followed * item) {
int ret = 0;
FILE * fp = fopen(item->filename, "r");
fseek(fp, 0, SEEK_END);
long end_position = ftell(fp);
if( end_position != item->last_position ) {
if(strcmp(item->filename, last_tailed)) { strcpy(last_tailed, item->filename); printf("\n** %s **:\n", item->filename); }
int start_position = item->last_position == -1 || item->last_position > end_position ? (end_position-CHAR_BACK > 0 ? end_position-CHAR_BACK : 0) : item->last_position;
fseek(fp, start_position, SEEK_SET);
int len = end_position - start_position;
char * buf = malloc(len+1);
fread(buf, len, 1, fp);
buf[len] = '\0';
printf("%s%s", len == CHAR_BACK ? "[...]" : "", buf);
free(buf);
item->last_position = end_position;
ret = 1;
}
fclose(fp);
return ret;
}
void fileRem(char * file) {
struct file_followed ** list = &file_list;
while(*list && strcmp((*list)->filename, file)) { list = &((*list)->next); }
if(*list) { struct file_followed * todel = *list; *list = (*list)->next; free(todel); }
}
int main(int argc, char ** argv) {
struct dirent **namelist;
struct stat statdesc;
struct timeval tv;
fd_set set;
int fd;
int wd;
int r;
// * Help
if(stat(argv[1], &statdesc) || !S_ISDIR(statdesc.st_mode)) { printf("[usage] %s dir-to-monitor\n", argv[0]); exit(EXIT_FAILURE); }
// * Init
chdir(argv[1]);
memset(last_tailed, 0, sizeof(last_tailed));
signal(SIGINT, stopCycle);
signal(SIGTERM, stopCycle);
// * Inotify
if( (fd = inotify_init()) < 0) { perror("inotify_init"); }
if( (wd = inotify_add_watch( fd, ".", IN_CREATE | IN_DELETE ) < 0)) { perror("inotify_add_watch"); }
// * File add recursively on dirscan
if( (r = scandir(".", &namelist, 0, alphasort)) < 0) { perror("scandir"); }
while (r--) { fileAdd(namelist[r]->d_name); free(namelist[r]); }
free(namelist);
// * Neverending cycle
while(cycle) {
// * Select on inotify
FD_ZERO(&set);
FD_SET(fd, &set);
tv.tv_sec = 0;
tv.tv_usec = 1000;
if( (r = select(fd+1, &set, NULL, NULL, &tv)) == -1) { perror("select"); }
// * New add or del on inotify
if(r) {
struct inotify_event * event;
char buf[1024];
if(read(fd, buf, 1024) <= 0) { perror("read"); }
event = (struct inotify_event *) buf;
if(event->mask & IN_CREATE) { fileAdd(event->name); }
else if(event->mask & IN_DELETE) { fileRem(event->name); }
}
// * Check for new tails
struct file_followed * list = file_list;
int tailers = 0;
while(list) { tailers += fileTail(list); list = list->next; }
if(!tailers) { usleep(500000); }
}
// * Stop inotify
inotify_rm_watch( fd, wd );
close(fd);
return EXIT_SUCCESS;
}
Solution 2:
I made changes to https://serverfault.com/a/542580/203373
to fix a couple of compile errors on my system (using Ubuntu linux).
I added casts to (struct file_followed*)
and (char*)
, and included
IN_MODIFY
in the add watch list to watch for modifications to current files. Added this line:
if(event->mask & IN_MODIFY) { fileMod(event->name, file_list); }
and the fileMod
function
void fileMod(char* fileName, struct file_followed* file_list)
to check if a modified file was truncated, and print out if it had been as well as update item->last_position = -1
so that it reprints the file.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/inotify.h>
#include <sys/stat.h>
#include <signal.h>
#include <dirent.h>
#include <linux/limits.h>
#define CHAR_BACK 500
// * File handler structure
struct file_followed { long last_position; char filename[NAME_MAX]; struct file_followed * next; };
struct file_followed * file_list = NULL;
// * To quit peacefully
int cycle = 1;
void stopCycle(int u) { cycle = 0; }
// * Last tailed filename
char last_tailed[NAME_MAX];
void fileAdd(char * file) {
struct file_followed ** list = &file_list;
struct stat statdesc;
if(stat(file, &statdesc) || !S_ISREG(statdesc.st_mode)) { return; }
while(*list) { list = &((*list)->next); }
*list = (struct file_followed*)malloc(sizeof(struct file_followed));
(*list)->last_position = -1;
strcpy((*list)->filename, file);
(*list)->next = NULL;
}
void fileMod(char* fileName, struct file_followed* file_list) {
struct file_followed* item = file_list;
while(item) {
if(strcmp(item->filename, fileName) == 0) {
FILE* fp = fopen(item->filename, "r");
fseek(fp, 0, SEEK_END);
long end_position = ftell(fp);
fclose(fp);
if (end_position <= item->last_position) {
printf("\n** %s truncated **\n", fileName);
item->last_position = -1;
}
usleep(100);
return;
}
item = item->next;
}
}
int fileTail(struct file_followed * item) {
int ret = 0;
FILE * fp = fopen(item->filename, "r");
fseek(fp, 0, SEEK_END);
long end_position = ftell(fp);
if( end_position != item->last_position ) {
if(strcmp(item->filename, last_tailed)) { strcpy(last_tailed, item->filename); printf("\n** %s **:\n", item->filename); }
int start_position = item->last_position == -1 || item->last_position > end_position ? (end_position-CHAR_BACK > 0 ? end_position-CHAR_BACK : 0) : item->last_position;
fseek(fp, start_position, SEEK_SET);
int len = end_position - start_position;
char * buf = (char*)malloc(len+1);
fread(buf, len, 1, fp);
buf[len] = '\0';
printf("%s%s", len == CHAR_BACK ? "[...]" : "", buf);
free(buf);
item->last_position = end_position;
ret = 1;
}
fclose(fp);
return ret;
}
void fileRem(char * file) {
struct file_followed ** list = &file_list;
while(*list && strcmp((*list)->filename, file)) { list = &((*list)->next); }
if(*list) { struct file_followed * todel = *list; *list = (*list)->next; free(todel); }
}
int main(int argc, char ** argv) {
struct dirent **namelist;
struct stat statdesc;
struct timeval tv;
fd_set set;
int fd;
int wd;
int r;
// * Help
if(stat(argv[1], &statdesc) || !S_ISDIR(statdesc.st_mode)) { printf("[usage] %s dir-to-monitor\n", argv[0]); exit(EXIT_FAILURE); }
// * Init
chdir(argv[1]);
memset(last_tailed, 0, sizeof(last_tailed));
signal(SIGINT, stopCycle);
signal(SIGTERM, stopCycle);
// * Inotify
if( (fd = inotify_init()) < 0) { perror("inotify_init"); }
if( (wd = inotify_add_watch( fd, ".", IN_CREATE | IN_MODIFY |IN_DELETE ) < 0)) { perror("inotify_add_watch"); }
// * File add recursively on dirscan
if( (r = scandir(".", &namelist, 0, alphasort)) < 0) { perror("scandir"); }
while (r--) { fileAdd(namelist[r]->d_name); free(namelist[r]); }
free(namelist);
// * Neverending cycle
while(cycle) {
// * Select on inotify
FD_ZERO(&set);
FD_SET(fd, &set);
tv.tv_sec = 0;
tv.tv_usec = 1000;
if( (r = select(fd+1, &set, NULL, NULL, &tv)) == -1) { perror("select"); }
// * New add or del on inotify
if(r) {
struct inotify_event * event;
char buf[1024];
if(read(fd, buf, 1024) <= 0) { perror("read"); }
event = (struct inotify_event *) buf;
if(event->mask & IN_MODIFY) { fileMod(event->name, file_list);}
else if(event->mask & IN_CREATE) { fileAdd(event->name); }
else if(event->mask & IN_DELETE) { fileRem(event->name); }
}
// * Check for new tails
struct file_followed * list = file_list;
int tailers = 0;
while(list) { tailers += fileTail(list); list = list->next; }
if(!tailers) { usleep(500000); }
}
// * Stop inotify
inotify_rm_watch( fd, wd );
close(fd);
return EXIT_SUCCESS;
}