Why can't embed commands like fg or bg in a shell script ? Post: 302306638

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Top Forums Shell Programming and Scripting Why can't embed commands like fg or bg in a shell script ? Post 302306638 by qiulang on Monday 13th of April 2009 11:10:35 AM

04-13-2009

Registered User

Thanks for the reply. With your input I further get the following information,

job control is by default turned off in non-interactive mode (shell script runs in non-interactive mode -- Bash Reference Manual). So to enable job control, we need set -m explicitly.
"Typically, Job Control is enabled for the interactive shell only. Non-interactive shells typically do not benefit from the added functionality of Job Control." sh(1) - standard and job control shell and command interpreter (man pages section 1: User Commands) - Sun Microsystems
It seems that I am not the only one feel confused about this statement , in a discussion in stackoverflow, Why can't I use job control in a bash script? - Stack Overflow, someone else asked "So why doesn't script-based job-control work, and what makes it a bad practice (aka 'stupid')?". Although there some answers for it, I still feel this controlling-terminal-job-control-foreground-background thing not so easy to get.
Initializing the Shell - The GNU C Library -- "A subshell that runs non-interactively cannot and should not support job control. ... this allows the non-interactive shell and its child processes to be treated as a single job by the parent shell." Even harder to get

So can someone further elaborate on this ?

Thanks!!

qiulang

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LEARN ABOUT MINIX

dh_installdeb

DH_INSTALLDEB(1)						     Debhelper							  DH_INSTALLDEB(1)

NAME

       dh_installdeb - install files into the DEBIAN directory

SYNOPSIS

       dh_installdeb [debhelperoptions]

DESCRIPTION

       dh_installdeb is a debhelper program that is responsible for installing files into the DEBIAN directories in package build directories with
       the correct permissions.

FILES

       package.postinst
       package.preinst
       package.postrm
       package.prerm
	   These maintainer scripts are installed into the DEBIAN directory.

	   Inside the scripts, the token #DEBHELPER# is replaced with shell script snippets generated by other debhelper commands.

       package.triggers
       package.shlibs
	   These control files are installed into the DEBIAN directory.

	   Note that package.shlibs is only installed in compat level 9 and earlier.  In compat 10, please use dh_makeshlibs(1).

       package.conffiles
	   This control file will be installed into the DEBIAN directory.

	   In v3 compatibility mode and higher, all files in the etc/ directory in a package will automatically be flagged as conffiles by this
	   program, so there is no need to list them manually here.

       package.maintscript
	   Lines in this file correspond to dpkg-maintscript-helper(1) commands and parameters.  However, the "maint-script-parameters" should not
	   be included as debhelper will add those automatically.

	   Example:

	       # Correct
	       rm_conffile /etc/obsolete.conf 0.2~ foo
	       # INCORRECT
	       rm_conffile /etc/obsolete.conf 0.2~ foo -- "$@"

	   In compat 10 or later, any shell metacharacters will be escaped, so arbitrary shell code cannot be inserted here.  For example, a line
	   such as "mv_conffile /etc/oldconffile /etc/newconffile" will insert maintainer script snippets into all maintainer scripts sufficient
	   to move that conffile.

	   It was also the intention to escape shell metacharacters in previous compat levels.	However, it did not work properly and as such it
	   was possible to embed arbitrary shell code in earlier compat levels.

	   The dh_installdeb tool will do some basic validation of some of the commands listed in this file to catch common mistakes.  The
	   validation is enabled as a warning since compat 10 and as a hard error in compat 12.

SEE ALSO

       debhelper(7)

       This program is a part of debhelper.

AUTHOR

       Joey Hess <joeyh@debian.org>

11.1.6ubuntu2							    2018-05-10							  DH_INSTALLDEB(1)

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