How can I get the source code for the linux utility tail?

Question

this command is really very useful but where I can get the source code to see what is going on inside .

thanks .

score 42 · Accepted Answer · edited Oct 01 '14 at 15:36

42

The tail utility is part of the coreutils on linux.

Source tarball: ftp://ftp.gnu.org/gnu/coreutils/coreutils-7.4.tar.gz
Source file: http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/tail.c

I've always found FreeBSD to have far clearer source code than the gnu utilities. So here's tail.c in the FreeBSD project:

http://svnweb.freebsd.org/csrg/usr.bin/tail/tail.c?view=markup

edited Oct 01 '14 at 15:36

patstuart

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answered Sep 17 '09 at 16:14

Stef

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+1 for diversity, even though the original question was about linux utility. – Michael Krelin - hacker Sep 17 '09 at 16:19
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I like how the linux version is several times longer than the BSD version. – Maxy-B Sep 04 '12 at 14:30
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The BSD version is shorter because the functions that do all the work aren't in that file. i.e.: follow(). – Ben L. Apr 27 '13 at 14:06

dmckee --- ex-moderator kitten · Answer 2 · 2009-09-17T16:25:18.100

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Poke around the uclinux site. Since they distributed the software, they are required to make the source available one way or another.

Or, you could read man fseek and guess at how it might be done.

NB-- See William's comments below, there are cases when you can't use seek.

edited Sep 17 '09 at 16:25

answered Sep 17 '09 at 16:10

dmckee --- ex-moderator kitten

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tail does not use fseek. If it did, it would not work on a stream (eg 'grep pat file | tail') – William Pursell Sep 17 '09 at 16:13
Hmm, never thought of that. Thanks. I have to think that it would still be faster when working with seekable input. – dmckee --- ex-moderator kitten Sep 17 '09 at 16:18
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This is not exactly true. `tail` doesn't *always* use seek ;-) – Michael Krelin - hacker Sep 17 '09 at 16:20

score 0 · Answer 3 · answered Sep 17 '09 at 16:14

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You might find it an interesting exercise to write your own. The vast majority of the Unix command-line tools are a page or so of fairly straightforward C code.

To just look at the code, the GNU CoreUtils sources are easily found on gnu.org or your favorite Linux mirror site.

answered Sep 17 '09 at 16:14

Mark Bessey

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I wrote a fairly complete set of tools for MS-DOS back when Linux was in its infancy. And while many are certainly straight forward, I would hesitate to say "a page' and wouldn't say a "vast majority". **find** and **ls** for example, were considerably more complex. – NVRAM Sep 17 '09 at 16:26
The core of most of the tools generally *is* short. But the argument processing and corner case handling can be a pain. – dmckee --- ex-moderator kitten Sep 17 '09 at 16:26
Yes, I probably should have said "many" tools are short & simple. GNU tail has a lot of options, so it probably doesn't fit into the "simple" category. The version of tail that most people would use (i.e. tail -xxx file, or tail -f file) would be pretty simple. – Mark Bessey Sep 17 '09 at 19:04

score -2 · Answer 4 · edited Oct 13 '17 at 11:09

/`*This example implements the option n of tail command.*/`

    #define _FILE_OFFSET_BITS 64
    #include <stdio.h>
    #include <stdlib.h>
    #include <fcntl.h>
    #include <errno.h>
    #include <unistd.h>
    #include <getopt.h>

    #define BUFF_SIZE 4096

    FILE *openFile(const char *filePath)
    {
      FILE *file;
      file= fopen(filePath, "r");
      if(file == NULL)
      {
        fprintf(stderr,"Error opening file: %s\n",filePath);
        exit(errno);
      }
      return(file);
    }

    void printLine(FILE *file, off_t startline)
    {
      int fd;
      fd= fileno(file);
      int nread;
      char buffer[BUFF_SIZE];
      lseek(fd,(startline + 1),SEEK_SET);
      while((nread= read(fd,buffer,BUFF_SIZE)) > 0)
      {
        write(STDOUT_FILENO, buffer, nread);
      }
    }

    void walkFile(FILE *file, long nlines)
    {
      off_t fposition;
      fseek(file,0,SEEK_END);
      fposition= ftell(file);
      off_t index= fposition;
      off_t end= fposition;
      long countlines= 0;
      char cbyte;

      for(index; index >= 0; index --)
      {
        cbyte= fgetc(file);
        if (cbyte == '\n' && (end - index) > 1)
        {
          countlines ++;
          if(countlines == nlines)
          {
        break;
          }
         }
        fposition--;
        fseek(file,fposition,SEEK_SET);
      }
      printLine(file, fposition);
      fclose(file);
    }

    int main(int argc, char *argv[])
    {
      FILE *file;
      file= openFile(argv[2]);
      walkFile(file, atol(argv[1]));
      return 0;
    }

    /*Note: take in mind that i not wrote code to parse input options and arguments, neither code to check if the lines number argument is really a number.*/

How can I get the source code for the linux utility tail?

4 Answers4

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