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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
Old 04-13-2009
Thanks for the reply. With your input I further get the following information,

  1. 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.
  2. "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
  3. It seems that I am not the only one feel confused about this statement Smilie, 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.
  4. 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 Smilie
So can someone further elaborate on this ?

Thanks!!
 

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ATF-SH(1)						    BSD General Commands Manual 						 ATF-SH(1)

NAME
atf-sh [-s shell] -- interpreter for shell-based test programs SYNOPSIS
atf-sh script DESCRIPTION
atf-sh is an interpreter that runs the test program given in script after loading the atf-sh(3) library. atf-sh is not a real interpreter though: it is just a wrapper around the system-wide shell defined by ATF_SHELL. atf-sh executes the inter- preter, loads the atf-sh(3) library and then runs the script. You must consider atf-sh to be a POSIX shell by default and thus should not use any non-standard extensions. The following options are available: -s shell Specifies the shell to use instead of the value provided by ATF_SHELL. ENVIRONMENT
ATF_LIBEXECDIR Overrides the builtin directory where atf-sh is located. Should not be overridden other than for testing purposes. ATF_PKGDATADIR Overrides the builtin directory where libatf-sh.subr is located. Should not be overridden other than for testing purposes. ATF_SHELL Path to the system shell to be used in the generated scripts. Scripts must not rely on this variable being set to select a specific interpreter. EXAMPLES
Scripts using atf-sh(3) should start with: #! /usr/bin/env atf-sh Alternatively, if you want to explicitly choose a shell interpreter, you cannot rely on env(1) to find atf-sh. Instead, you have to hardcode the path to atf-sh in the script and then use the -s option afterwards as a single parameter: #! /path/to/bin/atf-sh -s/bin/bash ENVIRONMENT
ATF_SHELL Path to the system shell to be used in the generated scripts. SEE ALSO
atf-sh(3) BSD
September 27, 2014 BSD
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