C小程序 - 模拟more

摘自《linux-unix编程实践》

#include    <stdio.h>
#include    <signal.h>
#include    <termios.h>

#define    LINELEN    512
#define    oops(s)  { perror(s); exit(1); }

void do_more(FILE *);
int  see_more(FILE *);

int main(int ac,char *av[])
{
    FILE    *fp;
    int    rv = 0;

    settings(0);
    if ( ac == 1 )
        do_more(stdin);
    else
        while ( --ac )
            if ( (fp=fopen(*++av,"r")) != NULL ) {
                do_more(fp) ;
                fclose(fp);
            }
            else {
                perror(*av);
                rv = 1;
                break;
            }
    settings(1);
    return rv;
}

/*
 *  * called for SIGINT and SIGQUIT
 *   * - Just reset terminal and get out
 *    */
void handler(int s)
{
    settings(1);
    exit(0);
}

/*
 *  * program settings are turned on and off here
 *   */
settings(int how)
{
    void handler(int);
    int    rv;

    static struct termios    term_orig;

    /* read settings */
    if ( how == 0 )
    {
        struct termios        term_new;

        rv = tcgetattr(0, &term_orig);    /* get settings */
        if ( rv == -1 )
            oops("getting settings");
        term_new = term_orig;
        term_new.c_lflag   &= ~ICANON;    /* noncanonical    */
        term_new.c_lflag   &= ~ECHO;    /* no echo     */
        term_new.c_cc[VMIN] = 1;    /* chr-by-chr    */

        rv = tcsetattr(0, TCSANOW, &term_new);
        if ( rv == -1 )
            oops("changing settings");

        signal(SIGINT,handler);
        signal(SIGQUIT,handler);
    }
    else
    {
        tcsetattr(0, TCSANOW, &term_orig);
    }
}

void do_more( FILE *fp )
/*
 *  *  read PAGELEN lines, then call see_more() for further instructions
 *   */
{
    char    line[LINELEN];
    FILE    *fp_tty;
    int    num_of_lines = 0;
    int    see_more(FILE *), reply;
    int    pagelen = screen_rows(1);

    fp_tty = fopen( "/dev/tty", "r" );       /* NEW: cmd stream   */
    if ( fp_tty == NULL )               /* if open fails     */
        exit(1);                           /* no use in running */

    while ( fgets( line, LINELEN, fp ) ){        /* more input    */
        if ( num_of_lines == pagelen ) {    /* full screen?    */
            reply = see_more(fp_tty);  /* NEW: pass FILE *  */
            if ( reply == 0 )        /*    n: done   */
                break;
            if ( reply == -1 )
                num_of_lines = 0;
            else
                num_of_lines -= reply;    /* reset count    */
        }
        if ( fputs( line, stdout )  == EOF )    /* show line    */
            exit(1);            /* or die    */
        num_of_lines++;                /* count it    */
    }
}

int see_more(FILE *cmd)                   /* NEW: accepts arg  */
/*
 *  *    print message, wait for response, return # of lines to advance
 *   *    q means no, space means yes, CR means one line
 *    *    Returns -1 for spacebar (ie. full screen)
 *     */
{
    int    c;

    printf("\033[7m more? \033[m");        /* reverse on a vt100    */
    while( (c=getc(cmd)) != EOF )        /* NEW: reads from tty  */
    {
        printf("\r       \r");        /* erase message    */
        if ( c == 'q' )            /* q -> N        */
            return 0;
        if ( c == ' ' )            /* ' ' => next page    */
            return -1;        /* -1 means full page    */
        if ( c == '\n' )        /* Enter key => 1 line    */
            return 1;
        printf("\033[7m more? \033[m");    /* put it back        */
    }
    return 0;
}

#include <sys/ioctl.h>

/*
 *  *  returns the number of rows associated with fd
 *   *  or 24 if that number cannot be determined
 *    */
int
screen_rows(fd)
{
    struct winsize wbuf;

    if ( ioctl(fd, TIOCGWINSZ, &wbuf) != -1 )
        return wbuf.ws_row;
    return 24;
}