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Full Discussion: Read command restarts at beginning of file
Top Forums Shell Programming and Scripting Read command restarts at beginning of file Post 302990288 by DJR on Tuesday 24th of January 2017 11:36:07 AM
Old 01-24-2017
Read command restarts at beginning of file
I am reading in a file in a Korn shell script. The file has one header row followed by possibly millions of data rows. I want to do one thing to the header row and write it out to a new output file, then something different to the data rows. My code looks like this:

Code:
read header < $infile 
    lineout=...$header...
echo $lineout >> $outfile
 
while read dataline
do
   lineout=....$dataline.....
   echo $lineout >> $outfile
done < $infile

But when I do this the while loop reads the first line in again - so I get the header line twice. The pointer goes back to the start of the file, or it closes and reopens, not sure what is going on. I know I could put the header logic in the while loop and just test for the first line and do that coding there. But I'd rather not have to do that test millions of times when I know I only need to process the first line differently. Why does the file reader not move to the next line? I assume the "done < $infile" part is forcing it to start at the beginning again. Anyway to make this work this way?
 

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LEARN ABOUT DEBIAN

dxf2vrml

DIME(1) 						      General Commands Manual							   DIME(1)

NAME

       dxf2vrml - program to convert .dxf formatted 3-D datasets to .VRML format.

SYNOPSIS

       dxf2vrml [infile][-ooutfile][-emaxerr][-f][-l]

DESCRIPTION

       This manual page documents briefly the dxf2vrml command.  (default infile is stdin, default outfile is stdout) This manual page was written
       for the Debian GNU/Linux distribution because the original program does not have a manual page.	Instead, it has documentation in  the  GNU
       Info format; see below.

       dxf2vrml is a program that...

OPTIONS

       These  programs	follow	the  usual  GNU  command  line	syntax, with long options starting with two dashes (`-').  A summary of options is
       included below.	For a complete description, see the Info files.

       infile default infile is stdin

       -o outfile,
	      default outfile is stdout

       -e,    Maximum error when tessellating curves

       -f,    Respect the $FILLMODE header variable

       -vrml2,
	      Write as vrml2. Default is vrml1

       -l,    Use layer color, ignore the color index

       -s,    Set sub parameter

       -h,    Show useage.

SEE ALSO

       files in: /usr/share/doc/libdime/, /usr/share/doc/libdime-dev/.
       The programs are documented fully by http://www.coin3d.org/lib/dime/, available via the Internet.

AUTHOR

       This manual page was written by A. Maitland Bottoms <bottoms@debian.org>, for the Debian GNU/Linux system (but may be used by others).

								 January 11, 2002							   DIME(1)
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