Shell advanced syntax? Post: 302463833

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Top Forums Shell Programming and Scripting Shell advanced syntax? Post 302463833 by Scott on Monday 18th of October 2010 02:26:58 PM

10-18-2010

Administrator Emeritus

Quote:

Originally Posted by alister

Every single command run on a UNIX/Linux/POSIX system will return an exit status. If that exit status is 0, the shell treats that as a boolean true. Any other exit status is treated as a boolean false.

Regards,
Alister

I certainly wouldn't challenge your assertion of that. But I would challenge any assertion that said return codes are always meaningful:

Code:

/root # yum install jiggery-pokery
Loaded plugins: fastestmirror, priorities
Determining fastest mirrors
 * addons: mirror.atrpms.net
 * base: mirror.switch.ch
 * extras: mirror.atrpms.net
 * updates: ftp.halifax.rwth-aachen.de
addons                                                   |  951 B     00:00     
addons/primary                                           |  202 B     00:00     
base                                                     | 2.1 kB     00:00     
base/primary_db                                          | 1.6 MB     00:01     
extras                                                   | 2.1 kB     00:00     
extras/primary_db                                        | 188 kB     00:00     
updates                                                  | 1.9 kB     00:00     
updates/primary_db                                       | 670 kB     00:00     
Setting up Install Process
No package jiggery-pokery available.
Nothing to do
/root # echo $?
0

Or perhaps alt's confusion is based on the interpretation of

Code:

if [[.....]] ; then
   [[ -f ... ]] && \
      export  ... || \
      { 
      echo ...; exit; 
      }

where the || relates not to the failure of the export command, but more to that of the test which precedes it?

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LEARN ABOUT DEBIAN

metalink

METALINK(1)						      General Commands Manual						       METALINK(1)

NAME

       metalink -- commandline metalink generator

SYNOPSIS

       metalink [input files]  [ < mirror list]

DESCRIPTION

       This manual page documents briefly the metalink command.

       This manual page was written for the Debian distribution because the original program does not have a manual page.

       metalink allows you to generate metalinks from a list of mirrors and a collection of files. The files are hashed and the resulting metalink
       is generated on the stdout.

OPTIONS

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

       -h	    --help
		 Produce a help message

		 --version
		 Print out the name and version.

		 --md5
		 Generate metalink from md5sum file(s).

		 --addpath path
		 Append a path to the mirrors ('/' is not checked)

		 --headerfile arg
		 Include file after the root element declaration.

		 --nomirrors
		 Don't read mirrors from stdin

		 --hashlist
		 List hashes only (implies nomirrors)

		 --desc arg
		 Add metalink description

		 -d arg
		 Include given digest

		 --mindigests
		 Include: md5 sha1

		 --somedigests
		 Include: md5 sha1 ed2k

		 --alldigests
		 Include all possible digests

       Supported algorithms are (-d options): md4 md5 sha1 sha256 sha384 sha512 rmd160 tiger crc32 ed2k gnunet sha1pieces

       Mirror lists are single line definitions according to: [location [preference] [type] % ] mirror base url

EXAMPLES

       http://example.com/ as a mirror: echo http://example.com | metalink -d md5 -d sha1 *

       http://example.com/ as a mirror with preference and location: echo us 10 % http://example.com | metalink -d md5 -d sha1 *

       http://example.com/ as a mirror with preference only: echo 0 10 % http://example.com | metalink -d md5 *

AUTHOR

       This manual page was written by A. Bram Neijt bneijt@gmail.com for the Debian system (but may be used by others).  Permission is granted to
       copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 any later  version  published	by
       the Free Software Foundation.

       On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL.

																       METALINK(1)

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