POSIX compliance... Post: 302976886

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Operating Systems OS X (Apple) POSIX compliance... Post 302976886 by Don Cragun on Thursday 7th of July 2016 02:24:13 PM

07-07-2016

Registered User

Some shells (such as bash and 1993 or later versions of ksh) provide:

Code:

for((n=1; n<=100; n++))
do	echo "process n=$n"
done

but this is an extension that is not yet specified by the standards. As you said, standard ways to do the same thing require an initialization step before the loop, such as in:

Code:

n=1
while [ $n -le 100 ]
do	echo "process n=$n"
	n=$((n + 1))
done

and in:

Code:

n=0
while [ $((++n <= 100)) -eq 1 ]
do	echo "process n=$n"
done

Note: As noted by Scrutinizer in post #8, the POSIX standards do not require $((++n)) to work. (It works with a recent bash and with a 1993 or later version of ksh, but is an extension to the requirements specified by the standards.)

Code:

n=0
while [ $(((n += 1) <= 100)) -eq 1 ]
do	echo "process n=$n"
done

should work in an POSIX-conforming shell.

Last edited by Don Cragun; 07-10-2016 at 04:56 PM.. Reason: Add note.

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shells

shells(4)							   File Formats 							 shells(4)

NAME

       shells - shell database

SYNOPSIS

       /etc/shells

DESCRIPTION

       The shells file contains a list of the shells on the system. Applications use this file to determine whether a shell is valid. See getuser-
       shell(3C). For each shell a single line should be present, consisting of the shell's path, relative to root.

       A hash mark (#) indicates the beginning of a comment; subsequent characters up to the end of the line are not interpreted by  the  routines
       which search the file. Blank lines are also ignored.

       The following default shells are used by utilities: /bin/bash, /bin/csh, /bin/jsh, /bin/ksh, /bin/ksh93, /bin/pfcsh, /bin/pfksh, /bin/pfsh,
       /bin/sh, /bin/tcsh, /bin/zsh, /sbin/jsh, /sbin/sh, /usr/bin/bash, /usr/bin/csh, /usr/bin/jsh, /usr/bin/ksh, /usr/bin/ksh93, /usr/bin/pfcsh,
       /usr/bin/pfksh, /usr/bin/pfsh, and /usr/bin/sh, /usr/bin/tcsh, /usr/bin/zsh, and /usr/sfw/bin/zsh. /etc/shells overrides the default list.

       Invalid shells in /etc/shells could cause unexpected behavior, such as being unable to log in by way of ftp(1).

FILES

       /etc/shells    list of shells on system

SEE ALSO

       vipw(1B), ftpd(1M), sendmail(1M), getusershell(3C), aliases(4)

SunOS 5.11							    20 Nov 2007 							 shells(4)

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