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/* Extract Lines
Usage: echo -x 10 2 7 100 | el data.txt
extracts lines 16, 2, 7, 256 from the file data.txt
*/
#include <stdlib.h>
#include "mystdlib.h"
#include <unistd.h>
// Our index into the already scanned lines.
// memory buffer is estimated to 1/32th of the
// indexed file's size, meaning each line
// containing approx 31 letters. If it hits the
// top, we increase in 1/32th steps
static unsigned char **index = NULL;
// this denotes the number of fields, NOT the
// memory occupied (would be a size_t, then!!!)
static long indexsize = 0;
// this specifies, how many lines have been indexed
// already, scanning always only happens to the
// last reqeusted line
static long indexfilled = 1;
// If set, the stream of linenums specified calls
// the first line number 0... *shiver*
static int zerobased = 0;
// This tells us, whether we need to scan for hex
// line numbers
static char *g_scanfmodifier = "%i";
// scans the text file for the requested line
// returns NULL, if line exceeds file's end
// Note: we will not extend the index too early
// to prevent huge numbers from stdin to steal our
// memory
static unsigned char * scanforline( MAP file, const long lineno, long *size ) {
unsigned char *scanline, *const e_o_f = file->addr + file->size;
static int alllinesscanned = 0;
*size = 0;
// lines start at 1
if( lineno < 1 ) return NULL;
// lines we already found can simply be returned
if( lineno < indexfilled ) {
*size = index[lineno] - index[lineno-1];
return index[lineno-1];
}
// if alllines were scanned, were either on
// or behind last line
if( alllinesscanned ) {
if( lineno == indexfilled ) {
*size = e_o_f - index[lineno-1];
return index[lineno-1];
}
return NULL;
}
// exploring undiscovered land...
scanline = index[indexfilled-1];
while( indexfilled <= lineno ) {
// scan for next line
while( ( scanline < e_o_f ) && ( *scanline++ != '\n' ));
// store pointer
if( scanline == e_o_f ) {
alllinesscanned = 1;
if( indexfilled == lineno ) {
*size = e_o_f - index[lineno-1];
return index[lineno-1];
} else
return NULL;
}
index[indexfilled++] = scanline;
// reallocate some memory
if( indexfilled == indexsize ) {
unsigned char ** newblock = (unsigned char**) realloc( index, sizeof(char *) * ( indexsize + file->size / 32 ) );
if( !newblock ) {
fputs( "Could not allocate memory, exiting.\n", stderr);
// unmap file and zero pointer
unmap_file( &file );
exit ( 1 );
}
indexsize += file->size / 32;
index = newblock;
}
}
*size = index[lineno] - index[lineno-1];
return index[lineno-1];
}
// Reads all characters up to the next white space
// from stdin, eof is treated as a white space
// If more than 13 characters without white space
// occur, we assume a too large line number and return
// 0 which is an invalid line (these start at 1) and will
// result in an empty line being printed
// Rationale:
// Since we wont support linenos greater 2^31 and this
// is 12 characters + leading 0 in octal, we stop parsing
// after 13 characters (technically, 001 is 01, but
// constructing such strings to annoy parser writers must
// be punished
static int acquire_lineno( int c ) {
char input[15];
int inputindex = 0, lineno;
while ( (c != EOF) && !isspace(c)) {
if( inputindex < 14 )
input[inputindex++] = (char)c;
c = getchar();
}
if( inputindex == 14 )
return 0;
input[inputindex] = 0;
// Try to read
if( sscanf( input, g_scanfmodifier, &lineno ) != 1 )
return 0;
return lineno + zerobased;
}
static void usage() {
fputs( "Usage: el [-0xh] filename < filenums\n", stderr);
}
int main( int argc, char **argv ) {
// Our handle to the mapped text file
MAP textfile = NULL;
int c;
while ((c = getopt(argc, argv, ":0x")) != -1) {
switch (c) {
case '0':
zerobased = 1;
break;
case 'x':
g_scanfmodifier = "%x";
break;
case 'h':
case '?':
default:
usage();
exit(1);
}
}
argc -= optind;
argv += optind;
if( argc != 1 ) { usage(); exit(1); }
// Map text file read only
if( (textfile = map_file( argv[0], 1 )) == NULL ) exit(1);
indexsize = textfile->size < 32 ? 32 : textfile->size / 32;
if( (index = malloc( sizeof(char *) * indexsize )) == NULL ) {
fputs( "Could not allocate memory, exiting.\n", stderr);
// unmap file and zero pointer
unmap_file( &textfile );
exit ( 1 );
}
// First line starts at begin of file.
index[0] = textfile->addr;
while( (c = getchar()) != EOF ) {
// get linenumber, pass on eof test char
long slen, lineno = acquire_lineno(c);
unsigned char *line = scanforline( textfile, lineno, &slen );
if( line && slen )
fwrite( line, slen, 1, stdout );
else
putchar('\n');
}
// unmap file and zero pointer
unmap_file( &textfile );
return 0;
}
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