BG(1)                      POSIX Programmer's Manual                     BG(1)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.


NNAAMMEE
       bg -- run jobs in the background

SSYYNNOOPPSSIISS
       bg [[_j_o_b___i_d...]]

DDEESSCCRRIIPPTTIIOONN
       If job control is enabled (see the description of _s_e_t --mm), the _b_g
       utility shall resume suspended jobs from the current environment (see
       _S_e_c_t_i_o_n _2_._1_2, _S_h_e_l_l _E_x_e_c_u_t_i_o_n _E_n_v_i_r_o_n_m_e_n_t) by running them as
       background jobs. If the job specified by _j_o_b___i_d is already a running
       background job, the _b_g utility shall have no effect and shall exit
       successfully.

       Using _b_g to place a job into the background shall cause its process ID
       to become ``known in the current shell execution environment'', as if
       it had been started as an asynchronous list; see _S_e_c_t_i_o_n _2_._9_._3_._1,
       _E_x_a_m_p_l_e_s.

OOPPTTIIOONNSS
       None.

OOPPEERRAANNDDSS
       The following operand shall be supported:

       _j_o_b___i_d    Specify the job to be resumed as a background job. If no
                 _j_o_b___i_d operand is given, the most recently suspended job
                 shall be used. The format of _j_o_b___i_d is described in the Base
                 Definitions volume of POSIX.1-2008, _S_e_c_t_i_o_n _3_._2_0_4, _J_o_b
                 _C_o_n_t_r_o_l _J_o_b _I_D.

SSTTDDIINN
       Not used.

IINNPPUUTT FFIILLEESS
       None.

EENNVVIIRROONNMMEENNTT VVAARRIIAABBLLEESS
       The following environment variables shall affect the execution of _b_g:

       _L_A_N_G      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1-2008, _S_e_c_t_i_o_n _8_._2, _I_n_t_e_r_n_a_t_i_o_n_a_l_i_z_a_t_i_o_n
                 _V_a_r_i_a_b_l_e_s for the precedence of internationalization
                 variables used to determine the values of locale categories.)

       _L_C___A_L_L    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       _L_C___C_T_Y_P_E  Determine the locale for the interpretation of sequences of
                 bytes of text data as characters (for example, single-byte as
                 opposed to multi-byte characters in arguments).

       _L_C___M_E_S_S_A_G_E_S
                 Determine the locale that should be used to affect the format
                 and contents of diagnostic messages written to standard
                 error.

       _N_L_S_P_A_T_H   Determine the location of message catalogs for the processing
                 of _L_C___M_E_S_S_A_G_E_S.

AASSYYNNCCHHRROONNOOUUSS EEVVEENNTTSS
       Default.

SSTTDDOOUUTT
       The output of _b_g shall consist of a line in the format:

           ""[[%%dd]] %%ss\\nn"",, <<_j_o_b_-_n_u_m_b_e_r>, <_c_o_m_m_a_n_d>

       where the fields are as follows:

       <_j_o_b_-_n_u_m_b_e_r>
                 A number that can be used to identify the job to the _w_a_i_t,
                 _f_g, and _k_i_l_l utilities. Using these utilities, the job can be
                 identified by prefixing the job number with ''%%''.

       <_c_o_m_m_a_n_d> The associated command that was given to the shell.

SSTTDDEERRRR
       The standard error shall be used only for diagnostic messages.

OOUUTTPPUUTT FFIILLEESS
       None.

EEXXTTEENNDDEEDD DDEESSCCRRIIPPTTIIOONN
       None.

EEXXIITT SSTTAATTUUSS
       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CCOONNSSEEQQUUEENNCCEESS OOFF EERRRROORRSS
       If job control is disabled, the _b_g utility shall exit with an error and
       no job shall be placed in the background.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       A job is generally suspended by typing the SUSP character (<control>-Z
       on most systems); see the Base Definitions volume of POSIX.1-2008,
       _C_h_a_p_t_e_r _1_1, _G_e_n_e_r_a_l _T_e_r_m_i_n_a_l _I_n_t_e_r_f_a_c_e.  At that point, _b_g can put the
       job into the background. This is most effective when the job is
       expecting no terminal input and its output has been redirected to non-
       terminal files. A background job can be forced to stop when it has
       terminal output by issuing the command:

           ssttttyy ttoossttoopp

       A background job can be stopped with the command:

           kkiillll --ss ssttoopp _j_o_b _I_D

       The _b_g utility does not work as expected when it is operating in its
       own utility execution environment because that environment has no
       suspended jobs. In the following examples:

           ...... || xxaarrggss bbgg
           ((bbgg))

       each _b_g operates in a different environment and does not share its
       parent shell's understanding of jobs. For this reason, _b_g is generally
       implemented as a shell regular built-in.

EEXXAAMMPPLLEESS
       None.

RRAATTIIOONNAALLEE
       The extensions to the shell specified in this volume of POSIX.1-2008
       have mostly been based on features provided by the KornShell. The job
       control features provided by _b_g, _f_g, and _j_o_b_s are also based on the
       KornShell. The standard developers examined the characteristics of the
       C shell versions of these utilities and found that differences exist.
       Despite widespread use of the C shell, the KornShell versions were
       selected for this volume of POSIX.1-2008 to maintain a degree of
       uniformity with the rest of the KornShell features selected (such as
       the very popular command line editing features).

       The _b_g utility is expected to wrap its output if the output exceeds the
       number of display columns.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._9_._3_._1, _E_x_a_m_p_l_e_s, _f_g, _k_i_l_l, _j_o_b_s, _w_a_i_t

       The Base Definitions volume of POSIX.1-2008, _S_e_c_t_i_o_n _3_._2_0_4, _J_o_b _C_o_n_t_r_o_l
       _J_o_b _I_D, _C_h_a_p_t_e_r _8, _E_n_v_i_r_o_n_m_e_n_t _V_a_r_i_a_b_l_e_s, _C_h_a_p_t_e_r _1_1, _G_e_n_e_r_a_l _T_e_r_m_i_n_a_l
       _I_n_t_e_r_f_a_c_e

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be obtained online
       at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                                BG(1)
