Files test How to recover a specific variable Post: 302981918

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Top Forums Shell Programming and Scripting Files test How to recover a specific variable Post 302981918 by rovf on Wednesday 21st of September 2016 08:27:17 AM

09-21-2016

Registered User

Quote:

Originally Posted by Arnaudh78

Thank for your reply, I use #!/bin/bash, So I work in Bash ? I'm beginner, I'm open at all.what do you recommend?

This depends on how you invoke your script.

If the script as executable rights, and you invoke it by typing the script name, the #! line defines, which language processor will be used to run your script. In your case, it is the bash executable stored in the /bin directory.

Alternatively, you can invoke the language processor to be used explicitly from the command line. For instance, if I write bash myfile, the file myfile should better be a bash script (and not zsh or ksh or awk....), as it will be executed under bash. The same applies to other languages - zsh, perl, ruby, ....

Now as for the recommendation. It is difficult to give a recommendation without starting a language war, because most programmers seem to be very picky when it comes to choosing one language over another, and everyone has his favorite pet, so note that I give here only my personal opinion, and others might advice you differently.

As for shell programming, after having had long experience with bash and a little bit experience with ksh, csh and tcsh, I turned to zsh, because I found that quite a few things are simpler to do in zsh than in the other languages. I yet have to see something which is easier to do in bash than in zsh (there must be something). The main drawback of zsh is that fewer people use it, so if you get stuck, you might have to search longer for someone to help. However, I got every zsh question answered by someone so far.

As second language, I tend to use Ruby (after having collected experience with awk, Perl, Python and Tcl), because I found it more expressive than the others and much easier to learn.

Of course one thing to consider it, where your script will run, and how much control you have on the software at the target machine. If I know that there is no zsh installed on the target machine, and I don't even have an account there, it would not be wise to deliver a zsh script. Having said this, even when using bash, you should make sure that you either develop your scripts with the same bash version than the one available on the target host, or write your scripts in a way that they will likely run under each version. This might turn out to be difficult, in particular for someone who doesn't have much experience yet.

If you run your programs only on your own machine, it is up to you what tools you choose.

rovf

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LEARN ABOUT DEBIAN

bup-margin

bup-margin(1)						      General Commands Manual						     bup-margin(1)

NAME

       bup-margin - figure out your deduplication safety margin

SYNOPSIS

       bup margin [options...]

DESCRIPTION

       bup margin  iterates  through  all  objects  in	your  bup repository, calculating the largest number of prefix bits shared between any two
       entries.  This number, n, identifies the longest subset of SHA-1 you could use and still encounter a collision between your object ids.

       For example, one system that was tested had a collection of 11 million objects (70 GB), and bup margin returned 45.  That  means  a  46-bit
       hash  would be sufficient to avoid all collisions among that set of objects; each object in that repository could be uniquely identified by
       its first 46 bits.

       The number of bits needed seems to increase by about 1 or 2 for every doubling of the number of objects.  Since SHA-1 hashes have 160 bits,
       that  leaves 115 bits of margin.  Of course, because SHA-1 hashes are essentially random, it's theoretically possible to use many more bits
       with far fewer objects.

       If you're paranoid about the possibility of SHA-1 collisions, you can monitor your repository by running bup margin occasionally to see	if
       you're getting dangerously close to 160 bits.

OPTIONS

       --predict
	      Guess  the offset into each index file where a particular object will appear, and report the maximum deviation of the correct answer
	      from the guess.  This is potentially useful for tuning an interpolation search algorithm.

       --ignore-midx
	      don't use .midx files, use only .idx files.  This is only really useful when used with --predict.

EXAMPLE

	      $ bup margin
	      Reading indexes: 100.00% (1612581/1612581), done.
	      40
	      40 matching prefix bits
	      1.94 bits per doubling
	      120 bits (61.86 doublings) remaining
	      4.19338e+18 times larger is possible

	      Everyone on earth could have 625878182 data sets
	      like yours, all in one repository, and we would
	      expect 1 object collision.

	      $ bup margin --predict
	      PackIdxList: using 1 index.
	      Reading indexes: 100.00% (1612581/1612581), done.
	      915 of 1612581 (0.057%)

SEE ALSO

       bup-midx(1), bup-save(1)

BUP

       Part of the bup(1) suite.

AUTHORS

       Avery Pennarun <apenwarr@gmail.com>.

Bup unknown-															     bup-margin(1)