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Full Discussion: replacing field in specific line in a file
Top Forums Shell Programming and Scripting replacing field in specific line in a file Post 302447955 by Corona688 on Tuesday 24th of August 2010 09:52:34 PM
Old 08-24-2010
Quote:
Originally Posted by vytenis
I would definitely like to hear about these 'better, faster and simpler ways'.
Here's the basic idea. Instead of creating and waiting for five seperate processes per line, you run read once. It's not even a process, just a builtin -- faster than awk/cut by a factor of 20 or so. And that's just if you're running awk/cut once per loop.
Code:
IFS=":" read PIN FIRST LAST ACCT BALANCE < filename

It reads data one line at a time from standard input(or whatever you redirect into standard input) and puts it into shell variables. It splits based on a special variable, IFS, which is usually space, but can be anything you want.

To loop through the whole file, you would do:

Code:
while IFS=":" read PIN FIRST LAST ACCT BALANCE
do
        # code to do something with the values here
done < filename

Now say you have a single line that you need to split into variables, but don't want to read it from file. Simple:

Code:
read A B C D E F <<< "words words flarg been words more words"

The <<< feeds it that txt on standard input without you having to create a file or pipe.
This User Gave Thanks to Corona688 For This Post:
vytenis
 

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LEARN ABOUT OPENSOLARIS

diffmk

diffmk(1)							   User Commands							 diffmk(1)

NAME

       diffmk - mark differences between versions of a troff input file

SYNOPSIS

       diffmk oldfile newfile markedfile

DESCRIPTION

       diffmk  compares  two versions of a file and creates a third version that includes "change mark" (.mc) commands for nroff(1) and  troff(1).
       oldfile and newfile are the old and new versions of the file. diffmk generates markedfile, which,  contains  the  text  from  newfile  with
       troff(1) "change mark" requests (.mc) inserted where  newfile differs from  oldfile. When markedfile is formatted, changed or inserted text
       is shown by  | at the right margin of each line. The position of deleted text is shown by a single *.

USAGE

       See largefile(5) for the description of the behavior of diffmk when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

EXAMPLES

       Example 1 An example of the diffmk command.

       diffmk can also be used in conjunction with the proper  troff requests to produce program listings with marked changes.	In  the  following
       command line:

	 example% diffmk old.c new.c marked.c ; nroff reqs marked.c | pr

       the file reqs contains the following troff requests:

	 .pl 1
	 .ll 77
	 .nf
	 .eo
	 .nh

       which eliminate page breaks, adjust the line length, set no-fill mode, ignore escape characters, and turn off hyphenation, respectively.

       If the characters  | and * are inappropriate, you might run  markedfile through	sed(1) to globally change them.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWdoc			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       diff(1), nroff(1), sed(1), troff(1), attributes(5), largefile(5)

BUGS

       Aesthetic  considerations  may  dictate	manual	adjustment of some output. File differences involving only formatting requests may produce
       undesirable output, that is, replacing .sp by .sp 2 will produce a "change mark" on the preceding or following line of output.

SunOS 5.11							    14 Sep 1992 							 diffmk(1)
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