Selective file copy

Selective file copy is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Copy part of input records to an output file.

Show how file processing as known from PL/I or COBOL can be implemented in the language of your choice.
Here, a file is not 'just' a sequence of bytes or lines but a sequence of recods (structured data). The structure is usually described by declarations contained in an INCLUDE file (PL/I) or COPY BOOK (COBOL).
The by name assignment is a little extra available in PL/I.
Data conversions may be necessary (as shown here for data element c.

ooRexx

<lang oorexx>/* REXX */ infile ="in.txt" outfile="out.txt"

s1=.copys~new(infile,outfile) loop i=1 to 5

 s1~~input~~output

end s1~close -- close streams (files) 'type' outfile

class copys

attribute a

attribute b

attribute c

attribute d

method init -- constructor

 expose instream outstream
 parse arg infile, outfile
 instream =.stream~new(infile)~~open
 outstream=.stream~new(outfile)~~open("replace")

method input -- read an input line

 expose instream a b c d
 parse value instream~linein with a +5 b +5 c +5 d +5

method output -- write an output line

 expose outstream a c
 outstream~lineout(a || c~c2x~left(2)'XXXXX')

method close -- close files

 expose instream outstream
 instream~close
 outstream~close</lang>

Output:

AA   01XXXXX
AAA  02XXXXX
AAAA 03XXXXX
AAAAA04XXXXX
AAAAA05XXXXX

PL/I

<lang pli>*process source attributes xref or(!);

copys: Proc Options(Main);
Dcl 1 s1 unal,
     2 a Char(5),
     2 b Char(5),
     2 c Bin Fixed(31),
     2 d Char(5);
Dcl 1 s2,
     2 a Char(5),
     2 c Pic'99',
     2 x Char(5) Init('XXXXX');
Dcl o1  Record Output;   /* create a test file */
Dcl in  Record Input;
Dcl out Record Output;
Do i=1 To 5;
  s1.a=repeat('A',i);
  s1.b=repeat('B',i);
  s1.c=i;
  s1.d=repeat('D',i);
  Write File(o1) From(s1);
  End;
Close File(o1);

On Endfile(in) Goto eoj;
Do i=1 By 1;             /* copy parts of the test file    */
  Read File(in) Into(s1);
  s2=s1, by name;        /* only fields a and c are copied */
  Write File(out) From(s2);
  End;
eoj:
End;

</lang>

Output:

AA   01XXXXX
AAA  02XXXXX
AAAA 03XXXXX
AAAAA04XXXXX
AAAAA05XXXXX

Rexx

Translation of: PL/I

<lang rexx>in='in.txt' out='out.txt'; 'erase' out Do While lines(in)>0

 l=linein(in)
 Parse Var l a +5 b +5 c +4 d +5
 chex=c2x(c)
 cpic=left(chex,2)
 call lineout out,a||cpic||'XXXXX'
 End

Call lineout in Call lineout out 'type' out</lang>

Output:

Using the test file produced by PL/I. The data conversion used for c is not very general!

AA   01XXXXX
AAA  02XXXXX
AAAA 03XXXXX
AAAAA04XXXXX
AAAAA05XXXXX