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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endusershell

getusershell(3C)					   Standard C Library Functions 					  getusershell(3C)

NAME

       getusershell, setusershell, endusershell - get legal user shells

SYNOPSIS

       #include <unistd.h>

       char *getusershell(void);

       void setusershell(void);

       void endusershell(void);

DESCRIPTION

       The  getusershell()  function  returns  a  pointer  to  a  legal  user  shell  as defined by the system manager in the file /etc/shells. If
       /etc/shells does not exist, the following locations of the standard system shells are used in its place:

	 /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/pfsh		    /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
	 /usr/bin/sh		    /usr/bin/tcsh
	 /usr/bin/zsh		    /usr/sfw/bin/zsh
	 /usr/xpg4/bin/sh

       The getusershell() function opens the file /etc/shells, if it exists, and returns the next entry in the list of shells.

       The setusershell() function rewinds the file or the list.

       The endusershell() function closes the file, frees any memory used by getusershell() and setusershell(), and rewinds the file /etc/shells.

RETURN VALUES

       The getusershell() function returns a null pointer on EOF.

BUGS

       All information is contained in memory that may be freed with a call to endusershell(), so it must be copied if it is to be saved.

NOTES

       Restricted shells should not be listed in /etc/shells.

SunOS 5.11							    1 Nov 2007							  getusershell(3C)

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endusershell