Why the results of these two code fragments are not the same? Post: 303030207

Sponsored Content

Top Forums Shell Programming and Scripting Why the results of these two code fragments are not the same? Post 303030207 by Don Cragun on Thursday 7th of February 2019 05:39:18 AM

02-07-2019

Registered User

I generally avoid eval, but have you considered making your shell script more like your C++ code?

Code:

#!/bin/sh
#set -xv
i=1
while [ $i -le $# ]
do	j=$((i + 1))
	while [ $j -le $# ]
	do	if eval [ \"\${$i}\" = \"\${$j}\" ]
		then	printf '\n%s (%d,%d)\n\nExiting...\n\n' \
			    'Error: Two or more arguments are the same:' \
			    $i $j >&2
			exit 1
		fi
		j=$((j + 1))
	done
	i=$((i + 1))
done

The while loops in the above script could be simplified to for loops that are accepted by many shells (including recent versions of bash and ksh) but they are extensions to the standards and, therefore, not available in several shells. The above code just uses standard utility interfaces and shell language constructs. For shells that accept these extensions, the below code looks even more like your C++ code.

Code:

#!/bin/sh
set -xv
for ((i = 1; i <= $#; i++))
do	for ((j = i + 1; j <= $#; j++))
	do	if eval [ \"\${$i}\" = \"\${$j}\" ]
		then	printf '\n%s (%d,%d)\n\nExiting...\n\n' \
			    "Error: Two or more arguments are the same:" \
			    $i $j >&2
			exit 1
		fi
	done
done

Note that both of these script write their error messages to the standard error output instead of to standard output and both of these script print the argument numbers of the first found pair of identical argument in their diagnostics.

Don Cragun

View Public Profile for Don Cragun

Find all posts by Don Cragun

8 More Discussions You Might Find Interesting

1. UNIX for Advanced & Expert Users

fragments in Solaris 8

When discussing inodes and data blocks, I know Solaris creates these data blocks with a total size of 8192b, divided into eight 1024b "fragments." It stores data in "contiguous" fragments and solaris doesn't allow a file to use portions of two different fragments. If the file size permits, then the...

2. Post Here to Contact Site Administrators and Moderators

results survey

Hi guys! I was wondering what the outcome was of your survey of a few months ago? One of the questions was if people were willing to pay for additional services like an own account, like username@unix.com with mail box, etc. Sorry if I missed the results if you had already posted them. Ivo

3. Solaris

ipfilter blocking ip fragments

For some reason ipfilter is blocking inbound fragmented ip packets (the packets are larger than the interface's MTU) that are encapsulating UDP segments. The connection works, so I know ipfilter is letting some traffic through, it is just a lot slower than it should be. Rules that allow the...

4. IP Networking

Solaris 11 Express NAT/Router IP Fragments

Upon replacing my linux router/server with a Solaris one I've noticed very poor network performance. The server itself has no issues connecting to the net, but clients using the server as a router are getting a lot of IP fragments as indicated from some packet sniffing I conducted. Here was my...

5. Shell Programming and Scripting

Can ctag and cscope support recording search results and displaying the history results ?

Hello , When using vim, can ctag and cscope support recording search results and displaying the history results ? Once I jump to one tag, I can use :tnext to jump to next tag, but how can I display the preview search result?

6. Shell Programming and Scripting

Why use different FS, the results is different?

# echo '1 2 3 ' | awk -F' ' '{print NF}' 3 # echo '1:2:3:' | awk -F':' '{print NF}' 4

7. Shell Programming and Scripting

Extract fragments from file

I have a .xml file that looks something like this : <measInfo> ......... string1 ......... </measInfo> <measInfo> ...... string2 ........ </measInfo> I want to extract only the 'chunk of file' from '<measInfo>' to '</measInfo>' containing string1 (or a certain string that I...

8. Shell Programming and Scripting

I want to add a variable for the results from the formula of one variable and results of another var

Good morning all, This is the file name in question OD_Orders_2019-02-19.csv I am trying to create a bash script to read into files with yesterdays date on the file name while retaining the rest of the files name. I would like for $y to equal, the name of the file with a formula output with...

LEARN ABOUT DEBIAN

vend::counterfile

Vend::CounterFile(3pm)					User Contributed Perl Documentation				    Vend::CounterFile(3pm)

NAME

       Vend::CounterFile - Persistent counter class

SYNOPSIS

	use Vend::CounterFile;
	$c = new Vend::CounterFile "COUNTER", "aa00";

	$id = $c->inc;
	open(F, ">F$id");

DESCRIPTION

       (This module is modified from Gisle Aas File::CounterFile to use
	Interchange's locking protocols -- lack of fcntl locking was causing
	counter problems.)

       This module implements a persistent counter class.  Each counter is represented by a separate file in the file system.  File locking is
       applied, so multiple processes might try to access the same counters at the same time without risk of counter destruction.

       You give the file name as the first parameter to the object constructor ("new").  The file is created if it does not exist.

       If the file name does not start with "/" or ".", then it is interpreted as a file relative to $Vend::CounterFile::DEFAULT_DIR.  The default
       value for this variable is initialized from the environment variable "TMPDIR", or /usr/tmp is no environment variable is defined.  You may
       want to assign a different value to this variable before creating counters.

       If you pass a second parameter to the constructor, that sets the initial value for a new counter.  This parameter only takes effect when
       the file is created (i.e. it does not exist before the call).

       When you call the "inc()" method, you increment the counter value by one. When you call "dec()" the counter value is decrementd.  In both
       cases the new value is returned.  The "dec()" method only works for numerical counters (digits only).

       You can peek at the value of the counter (without incrementing it) by using the "value()" method.

       The counter can be locked and unlocked with the "lock()" and "unlock()" methods.  Incrementing and value retrieval is faster when the
       counter is locked, because we do not have to update the counter file all the time.  You can query whether the counter is locked with the
       "locked()" method.

       There is also an operator overloading interface to the Vend::CounterFile object.  This means that you might use the "++" operator for
       incrementing the counter, "--" operator for decrementing and you can interpolate counters diretly into strings.

BUGS

       (This problem alleviated by this modified module)

       It uses flock(2) to lock the counter file.  This does not work on all systems.  Perhaps we should use the File::Lock module?

COPYRIGHT

       Copyright (c) 1995-1998 Gisle Aas. All rights reserved.	Modifications made by and copyright (C) 2002 Red Hat, Inc.  and (c) 2002-2007
       Interchange Development Group

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

       Gisle Aas <aas@sn.no>

perl v5.14.2							    2010-03-25						    Vend::CounterFile(3pm)