: ) wonderful world ( :

Grouping with sed:

$ cat nrs.txt
01
02
03
04
05
06
07
08
09
10
11
12
$ cat nrs.txt | sed -n -e 'N;s/\n/ /g;p'
01 02
03 04
05 06
07 08
09 10
11 12
$ cat nrs.txt | sed -n -e 'N;N;s/\n/ /g;p'
01 02 03
04 05 06
07 08 09
10 11 12
$ cat nrs.txt | sed -n -e 'N;N;N;s/\n/ /g;p'
01 02 03 04
05 06 07 08
09 10 11 12
$ cat nrs.txt | sed -n -e 'N;N;N;N;N;s/\n/ /g;p'
01 02 03 04 05 06
07 08 09 10 11 12
$

Good for the following task:

$ cat entries.txt
entry-1-data-1
entry-1-data-2
entry-2-data-1
entry-2-data-2
$ cat entries.txt | sed -n -e 'N;s/\n/ /;p'
entry-1-data-1 entry-1-data-2
entry-2-data-1 entry-2-data-2
$

Two long groups, removing elements (1st, 2nd):

$ cat nrs.txt | sed -n -e 'p;n'
01
03
05
07
09
11
$ cat nrs.txt | sed -n -e 'n;p'
02
04
06
08
10
12
$

In general case you have groups of length _k_ and the starting pattern is ‘n;n;…;n’. There’s k-1 number of letter n here. You can place letter p around the n-s, which is exactly k possibility. If there’s a p in position k0 then the k0-th element will be printed out.
So if you have 6 long groups and you want every fifth element:

$ cat nrs.txt | sed -n -e 'n;n;n;n;p;n'
05
11
$

Here’s the spec.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<?mso-application progid="Word.Document"?>
<pkg:package xmlns:pkg="http://schemas.microsoft.com/office/2006/xmlPackage">
  <pkg:part
    pkg:name="/_rels/.rels"
    pkg:contentType="application/vnd.openxmlformats-package.relationships+xml">
    <pkg:xmlData>
      <Relationships
        xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
        <Relationship
          Id="foo"
          Type=
"http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument"
          Target="/word/document.xml"/>
      </Relationships>
    </pkg:xmlData>
  </pkg:part>
  <pkg:part
    pkg:name="/word/document.xml"
    pkg:contentType=
"application/vnd.openxmlformats-officedocument.wordprocessingml.document.main+xml">
    <pkg:xmlData>
      <w:document
        xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main">
        <w:body>
          <w:p>
            <w:r>
              <w:t>Hello World</w:t>
              <w:br />
              <w:yearLong />
            </w:r>
          </w:p>
        </w:body>
      </w:document>
    </pkg:xmlData>
  </pkg:part>
</pkg:package>

$ cat seconds.txt
120
123
$ cat seconds.txt | sed 's/$/ 60 ~ 0 !=r +/' | sed '1i[1+] sr 0' | sed '$ap' | dc
5
$

Please note that you cannot copy-paste the Makefile below.

afroid-laptop% ls
lexer.l  Makefile  parser.y
afroid-laptop% cat * | wc -l
77
afroid-laptop% cat -A Makefile
all:^Icompiler$
$
compiler:^Iparser.tab.o lex.yy.o$
^Igcc -o $@ parser.tab.o lex.yy.o -lm -lfl$
$
parser.tab.o:^Iparser.y$
^Ibison -dv parser.y$
^Igcc -c parser.tab.c$
$
lex.yy.o:^Ilexer.l parser.tab.o$
^Iflex lexer.l$
^Igcc -c lex.yy.c$
$
clean:$
^Irm -rf lex.yy.c lex.yy.o parser.tab.o parser.tab.c parser.tab.h parser.output compiler$
afroid-laptop% cat lexer.l
%{
#include
#include "parser.tab.h"
%}

DIGIT [0-9]
ALPHA [a-zA-Z]
WS [ \n\t]

%%

{DIGIT}+ { yylval.intval = atoi(yytext); return NUMBER; }
{ALPHA}+ { yylval.id = (char *) strdup(yytext); return IDENTIFIER; }
{WS}+    {}

%%
int yywrap (void)
{
}

afroid-laptop% cat parser.y
%{
#include
#include

extern FILE *yyin;
extern FILE *yyout;
%}

%union
{
  int intval;
  char* id;
}

%start S
%token  NUMBER
%token  IDENTIFIER

%%

S:
  /* empty */
| IDENTIFIER S NUMBER { fprintf (yyout, "let %s = %d;\n", $1, $3); }

%%

main (int argc, char **argv)
{
  char out[1024];
  ++argv; --argc;
  yyin = fopen (argv[0], "r");
  strcpy(out,argv[0]);
  strcat(out,".out");
  yyout = fopen (out, "w");
  yyparse ();
  printf ("Parse Completed\n");
}

yyerror (char *s)
{
  printf("error\n");
}
afroid-laptop% cat > test.src << EOF
heredoc> a b c 1 2 3
heredoc> EOF
afroid-laptop% make
bison -dv parser.y
gcc -c parser.tab.c
flex lexer.l
gcc -c lex.yy.c
gcc -o compiler parser.tab.o lex.yy.o -lm -lfl
afroid-laptop% ./compiler test.src
Parse Completed
afroid-laptop% cat test.src.out
let c = 1;
let b = 2;
let a = 3;
afroid-laptop%