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Top Forums UNIX for Dummies Questions & Answers subshell & background function Post 34796 by LivinFree on Wednesday 12th of March 2003 04:21:16 PM
Old 03-12-2003
The above comments are very important to understand, but a subshell will actually spawn a new shell process. For example, time the two following scripts to see which is faster:
#1
Code:
#! /bin/ksh
n=0
until (( n == 1000 )); do
     print Huh? >/dev/null
     ((n=n+1))
done

#2
Code:
#! /bin/ksh
n=0
until (( n == 1000 )); do
     ( print Huh? >/dev/null ; )
     ((n=n+1))
done

I should mention that I cannot test this at the moment, so I might be giving a bad example...
 

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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/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/pfcsh /usr/bin/pfksh /usr/bin/pfsh /usr/bin/sh /usr/bin/tcsh /usr/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. SunOS 5.10 30 Aug 2004 getusershell(3C)
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