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Top Forums Shell Programming and Scripting Inserting Header to another file Post 302925011 by Corona688 on Thursday 13th of November 2014 01:47:09 PM
Old 11-13-2014
Quote:
Originally Posted by gvkumar25
Instead what I taught is adding a single line to 20GB data is much faster.
Files do not work that way, you can't insert in the middle. That's why we have text editors to do it for us.

If whatever's using this huge file can read from standard input, you can skip editing the file, just add it to the stream -- print it first, then the rest of the file.

Code:
(       echo "header line"
        exec cat hugefile ) | programwhichuseshugefile


Last edited by Corona688; 11-13-2014 at 02:53 PM..
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CAT(1)							      General Commands Manual							    CAT(1)

NAME
cat, read, nobs - catenate files SYNOPSIS
cat [ file ... ] read [ -m ] [ -n nline ] [ file ... ] nobs [ file ... ] DESCRIPTION
Cat reads each file in sequence and writes it on the standard output. Thus cat file prints a file and cat file1 file2 >file3 concatenates the first two files and places the result on the third. If no file is given, cat reads from the standard input. Output is buffered in blocks matching the input. Read copies to standard output exactly one line from the named file, default standard input. It is useful in interactive rc(1) scripts. The -m flag causes it to continue reading and writing multiple lines until end of file; -n causes it to read no more than nline lines. Read always executes a single write for each line of input, which can be helpful when preparing input to programs that expect line-at-a- time data. It never reads any more data from the input than it prints to the output. Nobs copies the named files to standard output except that it removes all backspace characters and the characters that precede them. It is useful to use as $PAGER with the Unix version of man(1) when run inside a win (see acme(1)) window. SOURCE
/src/cmd/cat.c /src/cmd/read.c /bin/nobs SEE ALSO
cp(1) DIAGNOSTICS
Read exits with status eof on end of file or, in the -n case, if it doesn't read nlines lines. BUGS
Beware of and which destroy input files before reading them. CAT(1)
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