便捷指令tail -f 升级为tailf

创建文件tailf.c：vim /usr/local/tailf.c

/* tailf.c -- tail a log file and then follow it  
* Created: Tue Jan  9 15:49:21 1996 by faith@acm.org  
* Copyright 1996, 2003 Rickard E. Faith (faith@acm.org)  
*  
* Permission is hereby granted, free of charge, to any person obtaining a  
* copy of this software and associated documentation files (the "Software"),  
* to deal in the Software without restriction, including without limitation  
* the rights to use, copy, modify, merge, publish, distribute, sublicense,  
* and/or sell copies of the Software, and to permit persons to whom the  
* Software is furnished to do so, subject to the following conditions:  
*  
* The above copyright notice and this permission notice shall be included  
* in all copies or substantial portions of the Software.  
*  
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR  
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,  
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL  
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR  
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,  
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR  
* OTHER DEALINGS IN THE SOFTWARE.  
*   
* less -F and tail -f cause a disk access every five seconds.  This  
* program avoids this problem by waiting for the file size to change.  
* Hence, the file is not accessed, and the access time does not need to be  
* flushed back to disk.  This is sort of a "stealth" tail.  
*/   

#include <stdio.h>   
#include <stdlib.h>   
#include <unistd.h>   
#include <malloc.h>   
#include <sys/stat.h>   
//#include "nls.h"   
#define _(s) s   

static size_t filesize(const char *filename)   
{   
    struct stat sb;   

    if (!stat(filename, &sb)) return sb.st_size;   
    return 0;   
}   

static void tailf(const char *filename, int lines)   
{   
    char **buffer;   
    int  head = 0;   
    int  tail = 0;   
    FILE *str;   
    int  i;   

    if (!(str = fopen(filename, "r"))) {   
        fprintf(stderr, _("Cannot open \"%s\" for read\n"), filename);   
        perror("");   
        exit(1);   
    }   

    buffer = malloc(lines * sizeof(*buffer));   
    for (i = 0; i < lines; i++) buffer[i] = malloc(BUFSIZ + 1);   

    while (fgets(buffer[tail], BUFSIZ, str)) {   
        if (++tail >= lines) {   
        tail = 0;   
        head = 1;   
    }   
    }   

    if (head) {   
        for (i = tail; i < lines; i++) fputs(buffer[i], stdout);   
        for (i = 0; i < tail; i++)     fputs(buffer[i], stdout);   
    } else {   
        for (i = head; i < tail; i++)  fputs(buffer[i], stdout);   
    }   
    fflush(stdout);   

    for (i = 0; i < lines; i++) free(buffer[i]);   
    free(buffer);   
}   

  int main(int argc, char **argv)   
{   
    char       buffer[BUFSIZ];   
    size_t     osize, nsize;   
    FILE       *str;   
    const char *filename;   
    int        count;   

    //setlocale(LC_ALL, "");   
    //bindtextdomain(PACKAGE, LOCALEDIR);   
    //textdomain(PACKAGE);   

    if (argc != 2) {   
        fprintf(stderr, _("Usage: tailf logfile\n"));   
        exit(1);   
    }   

    filename = argv[1];   

    tailf(filename, 10);   

    for (osize = filesize(filename);;) {   
        nsize = filesize(filename);   
        if (nsize != osize) {   
        if (!(str = fopen(filename, "r"))) {   
            fprintf(stderr, _("Cannot open \"%s\" for read\n"), filename);   
            perror(argv[0]);   
            exit(1);   
        }   
        if (!fseek(str, osize, SEEK_SET))   
            while ((count = fread(buffer, 1, sizeof(buffer), str)) > 0)   
                    fwrite(buffer, 1, count, stdout);   
        fflush(stdout);   
        fclose(str);   
        osize = nsize;   
    }   
        usleep(250000);     /* 250mS */   
    }   
    return 0;   
}

cd /usr/local
gcc -Wall -o /usr/bin/tailf tailf.c