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Full Discussion: Make script faster
Top Forums Shell Programming and Scripting Make script faster Post 302584122 by rbatte1 on Thursday 22nd of December 2011 08:26:09 AM
Old 12-22-2011
The main reason is that your original had the following logic:-
  1. Start a process to read a line from the input
  2. Start a process to perform the cut *1
  3. Do a compare looking for value 27
  4. If we match, start a process for another cut *2
  5. Display the result
  6. Start from top to read next line
For a 400 line file, you are forcing 400 cut processes to be run for *1 and another set for the cut in *2
Depending on your shell, you might start 400 read processes, plus 400 echo statements in *1 and more for *2 for each line matching value 27.

All of this generates vast amounts of work just in the overheads. I'm not very good with awk myself but it all runs in a single process so is excellent if you can invest the time to get into the syntax. My variation removed many of these processes, but probably could still be improved. Every process launch requires memory to be allocated, perhaps logs to be written, paging/swap space to be altered etc, so before it actually does anything, there is a significant processing overhead - and then there may be end-of-process overheads too.

The use of the cat at the front makes it more readable for some, although I'm sure purists may not agree. I suppose it depends how you describe your logic in your mind before writing code. I just tried to follow your logic with a few tweaks so it doesn't become too different and need documentation or lots of work on your part to decipher, but it's the difference between thinking:-
  1. Working on this file, I will do these things to it, versus
  2. Do these things on this input file


I hope that this clarifies and helps,

Robin
Liverpool/Blackburn
UK
 

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LEARN ABOUT NETBSD

set_color

set_color(1)							       fish							      set_color(1)

NAME

       set_color - set_color - set the terminal color

set_color - set the terminal color
   Synopsis
       set_color [-v --version] [-h --help] [-b --background COLOR] [COLOR]

   Description
       Change the foreground and/or background color of the terminal. COLOR is one of black, red, green, brown, yellow, blue, magenta, purple,
       cyan, white and normal.

       o -b, --background Set the background color

       o -c, --print-colors Prints a list of all valid color names

       o -h, --help Display help message and exit

       o -o, --bold Set bold or extra bright mode

       o -u, --underline Set underlined mode

       o -v, --version Display version and exit

       Calling set_color normal will set the terminal color to whatever is the default color of the terminal.

       Some terminals use the --bold escape sequence to switch to a brighter color set. On such terminals, set_color white will result in a grey
       font color, while set_color --bold white will result in a white font color.

       Not all terminal emulators support all these features. This is not a bug in set_color but a missing feature in the terminal emulator.

       set_color uses the terminfo database to look up how to change terminal colors on whatever terminal is in use. Some systems have old and
       incomplete terminfo databases, and may lack color information for terminals that support it. Download and install the latest version of
       ncurses and recompile fish against it in order to fix this issue.

Version 1.23.1							  Sun Jan 8 2012						      set_color(1)
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