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23 <center><font size="2">The Open Group Base Specifications Issue 8<br>
24 IEEE Std 1003.1-2024<br>
25 Copyright © 2001-2024 The IEEE and The Open Group</font></center>
26 <hr size="2" noshade>
27 <a name="top" id="top"></a> <a name="bg" id="bg"></a> <a name="tag_20_10" id="tag_20_10"></a><!-- bg -->
28 <h4 class="mansect"><a name="tag_20_10_01" id="tag_20_10_01"></a>NAME</h4>
29 <blockquote>bg — run jobs in the background</blockquote>
30 <h4 class="mansect"><a name="tag_20_10_02" id="tag_20_10_02"></a>SYNOPSIS</h4>
31 <blockquote class="synopsis">
32 <div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt=
33 "[Option Start]" border="0"> bg</tt> <b>[</b><i>job_id</i><tt>...</tt><b>]</b> <tt><img src="../images/opt-end.gif" alt=
34 "[Option End]" border="0"></tt></code></div>
35 </blockquote>
36 <h4 class="mansect"><a name="tag_20_10_03" id="tag_20_10_03"></a>DESCRIPTION</h4>
37 <blockquote>
38 <p>If job control is enabled (see the description of <a href="../utilities/V3_chap02.html#set"><i>set</i></a> <b>-m</b>), the shell
39 is interactive, and the current shell execution environment (see <a href="../utilities/V3_chap02.html#tag_19_13"><i>2.13 Shell
40 Execution Environment</i></a> ) is not a subshell environment, the <i>bg</i> utility shall resume suspended jobs from the current
41 shell execution environment by running them as background jobs, as described in <a href=
42 "../utilities/V3_chap02.html#tag_19_11"><i>2.11 Job Control</i></a> ; it may also do so if the shell is non-interactive or the
43 current shell execution environment is a subshell environment. If the job specified by <i>job_id</i> is already a running
44 background job, the <i>bg</i> utility shall have no effect and shall exit successfully.</p>
45 </blockquote>
46 <h4 class="mansect"><a name="tag_20_10_04" id="tag_20_10_04"></a>OPTIONS</h4>
47 <blockquote>
48 <p>None.</p>
49 </blockquote>
50 <h4 class="mansect"><a name="tag_20_10_05" id="tag_20_10_05"></a>OPERANDS</h4>
51 <blockquote>
52 <p>The following operand shall be supported:</p>
53 <dl compact>
54 <dd></dd>
55 <dt><i>job_id</i></dt>
56 <dd>Specify the job to be resumed as a background job. If no <i>job_id</i> operand is given, the most recently suspended job shall
57 be used. The format of <i>job_id</i> is described in XBD <a href="../basedefs/V1_chap03.html#tag_03_182"><i>3.182 Job ID</i></a>
58 .</dd>
59 </dl>
60 </blockquote>
61 <h4 class="mansect"><a name="tag_20_10_06" id="tag_20_10_06"></a>STDIN</h4>
62 <blockquote>
63 <p>Not used.</p>
64 </blockquote>
65 <h4 class="mansect"><a name="tag_20_10_07" id="tag_20_10_07"></a>INPUT FILES</h4>
66 <blockquote>
67 <p>None.</p>
68 </blockquote>
69 <h4 class="mansect"><a name="tag_20_10_08" id="tag_20_10_08"></a>ENVIRONMENT VARIABLES</h4>
70 <blockquote>
71 <p>The following environment variables shall affect the execution of <i>bg</i>:</p>
72 <dl compact>
73 <dd></dd>
74 <dt><i>LANG</i></dt>
75 <dd>Provide a default value for the internationalization variables that are unset or null. (See XBD <a href=
76 "../basedefs/V1_chap08.html#tag_08_02"><i>8.2 Internationalization Variables</i></a> for the precedence of internationalization
77 variables used to determine the values of locale categories.)</dd>
78 <dt><i>LC_ALL</i></dt>
79 <dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
80 <dt><i>LC_CTYPE</i></dt>
81 <dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
82 opposed to multi-byte characters in arguments).</dd>
83 <dt><i>LC_MESSAGES</i></dt>
84 <dd><br>
85 Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.</dd>
86 <dt><i>NLSPATH</i></dt>
87 <dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
88 Determine the location of messages objects and message catalogs. <img src="../images/opt-end.gif" alt="[Option End]" border=
89 "0"></dd>
90 </dl>
91 </blockquote>
92 <h4 class="mansect"><a name="tag_20_10_09" id="tag_20_10_09"></a>ASYNCHRONOUS EVENTS</h4>
93 <blockquote>
94 <p>Default.</p>
95 </blockquote>
96 <h4 class="mansect"><a name="tag_20_10_10" id="tag_20_10_10"></a>STDOUT</h4>
97 <blockquote>
98 <p>The output of <i>bg</i> shall consist of a line in the format:</p>
99 <pre>
100 <tt>"[%d] %s\n", <</tt><i>job-number</i><tt>>, <</tt><i>command</i><tt>>
101 </tt></pre>
102 <p>where the fields are as follows:</p>
103 <dl compact>
104 <dd></dd>
105 <dt><<i>job-number</i>></dt>
106 <dd>A number that can be used to identify the job to the <a href="../utilities/wait.html"><i>wait</i></a>, <a href=
107 "../utilities/fg.html"><i>fg</i></a>, and <a href="../utilities/kill.html"><i>kill</i></a> utilities. Using these utilities, the
108 job can be identified by prefixing the job number with <tt>'%'</tt>.</dd>
109 <dt><<i>command</i>></dt>
110 <dd>The associated command that was given to the shell.</dd>
111 </dl>
112 </blockquote>
113 <h4 class="mansect"><a name="tag_20_10_11" id="tag_20_10_11"></a>STDERR</h4>
114 <blockquote>
115 <p>The standard error shall be used only for diagnostic messages.</p>
116 </blockquote>
117 <h4 class="mansect"><a name="tag_20_10_12" id="tag_20_10_12"></a>OUTPUT FILES</h4>
118 <blockquote>
119 <p>None.</p>
120 </blockquote>
121 <h4 class="mansect"><a name="tag_20_10_13" id="tag_20_10_13"></a>EXTENDED DESCRIPTION</h4>
122 <blockquote>
123 <p>None.</p>
124 </blockquote>
125 <h4 class="mansect"><a name="tag_20_10_14" id="tag_20_10_14"></a>EXIT STATUS</h4>
126 <blockquote>
127 <p>The following exit values shall be returned:</p>
128 <dl compact>
129 <dd></dd>
130 <dt> 0</dt>
131 <dd>Successful completion.</dd>
132 <dt>>0</dt>
133 <dd>An error occurred.</dd>
134 </dl>
135 </blockquote>
136 <h4 class="mansect"><a name="tag_20_10_15" id="tag_20_10_15"></a>CONSEQUENCES OF ERRORS</h4>
137 <blockquote>
138 <p>If job control is disabled, the <i>bg</i> utility shall exit with an error and no job shall be placed in the background.</p>
139 </blockquote>
140 <hr>
141 <div class="box"><em>The following sections are informative.</em></div>
142 <h4 class="mansect"><a name="tag_20_10_16" id="tag_20_10_16"></a>APPLICATION USAGE</h4>
143 <blockquote>
144 <p>This utility is required to be intrinsic. See <a href="../utilities/V3_chap01.html#tag_18_07"><i>1.7 Intrinsic Utilities</i></a>
145 for details.</p>
146 <p>A job is generally suspended by typing the SUSP character (<control>-Z on most systems); see XBD <a href=
147 "../basedefs/V1_chap11.html#tag_11"><i>11. General Terminal Interface</i></a> . At that point, <i>bg</i> can put the job into the
148 background. This is most effective when the job is expecting no terminal input and its output has been redirected to non-terminal
149 files. A background job can be forced to stop when it has terminal output by issuing the command:</p>
150 <pre>
151 <tt>stty tostop
152 </tt></pre>
153 <p>A background job can be stopped with the command:</p>
154 <pre>
155 <tt>kill -s stop </tt><i>job ID</i><tt>
156 </tt></pre>
157 <p>The <i>bg</i> utility does not work as expected when it is operating in its own utility execution environment because that
158 environment has no suspended jobs. In the following examples:</p>
159 <pre>
160 <tt>... | xargs bg
161 (bg)
162 </tt></pre>
163 <p>each <i>bg</i> operates in a different environment and does not share its parent shell's understanding of jobs. For this reason,
164 <i>bg</i> is generally implemented as a shell regular built-in.</p>
165 </blockquote>
166 <h4 class="mansect"><a name="tag_20_10_17" id="tag_20_10_17"></a>EXAMPLES</h4>
167 <blockquote>
168 <p>None.</p>
169 </blockquote>
170 <h4 class="mansect"><a name="tag_20_10_18" id="tag_20_10_18"></a>RATIONALE</h4>
171 <blockquote>
172 <p>The extensions to the shell specified in this volume of POSIX.1-2024 have mostly been based on features provided by the
173 KornShell. The job control features provided by <i>bg</i>, <a href="../utilities/fg.html"><i>fg</i></a>, and <a href=
174 "../utilities/jobs.html"><i>jobs</i></a> are also based on the KornShell. The standard developers examined the characteristics of
175 the C shell versions of these utilities and found that differences exist. Despite widespread use of the C shell, the KornShell
176 versions were selected for this volume of POSIX.1-2024 to maintain a degree of uniformity with the rest of the KornShell features
177 selected (such as the very popular command line editing features).</p>
178 <p>The <i>bg</i> utility is expected to wrap its output if the output exceeds the number of display columns.</p>
179 <p>The <i>bg</i> and <a href="../utilities/fg.html"><i>fg</i></a> utilities are not symmetric as regards the list of process IDs
180 known in the current shell execution environment. Whereas <a href="../utilities/fg.html"><i>fg</i></a> removes a process ID from
181 this list, <i>bg</i> has no need to add one to this list when it resumes execution of a suspended job in the background, because
182 this has already been done by the shell when the suspended background job was created (see <a href=
183 "../utilities/V3_chap02.html#tag_19_11"><i>2.11 Job Control</i></a> ).</p>
184 </blockquote>
185 <h4 class="mansect"><a name="tag_20_10_19" id="tag_20_10_19"></a>FUTURE DIRECTIONS</h4>
186 <blockquote>
187 <p>None.</p>
188 </blockquote>
189 <h4 class="mansect"><a name="tag_20_10_20" id="tag_20_10_20"></a>SEE ALSO</h4>
190 <blockquote>
191 <p><a href="../utilities/V3_chap02.html#tag_19_09_03_02"><i>2.9.3.1 Asynchronous AND-OR Lists</i></a> , <a href=
192 "../utilities/fg.html#"><i>fg</i></a> , <a href="../utilities/kill.html#tag_20_64"><i>kill</i></a> , <a href=
193 "../utilities/jobs.html#"><i>jobs</i></a> , <a href="../utilities/wait.html#tag_20_147"><i>wait</i></a></p>
194 <p>XBD <a href="../basedefs/V1_chap03.html#tag_03_182"><i>3.182 Job ID</i></a> , <a href="../basedefs/V1_chap08.html#tag_08"><i>8.
195 Environment Variables</i></a> , <a href="../basedefs/V1_chap11.html#tag_11"><i>11. General Terminal Interface</i></a></p>
196 </blockquote>
197 <h4 class="mansect"><a name="tag_20_10_21" id="tag_20_10_21"></a>CHANGE HISTORY</h4>
198 <blockquote>
199 <p>First released in Issue 4.</p>
200 </blockquote>
201 <h4 class="mansect"><a name="tag_20_10_22" id="tag_20_10_22"></a>Issue 6</h4>
202 <blockquote>
203 <p>This utility is marked as part of the User Portability Utilities option.</p>
204 <p>The JC margin marker on the SYNOPSIS is removed since support for Job Control is mandatory in this version. This is a FIPS
205 requirement.</p>
206 </blockquote>
207 <h4 class="mansect"><a name="tag_20_10_23" id="tag_20_10_23"></a>Issue 7</h4>
208 <blockquote>
209 <p>SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.</p>
210 </blockquote>
211 <h4 class="mansect"><a name="tag_20_10_24" id="tag_20_10_24"></a>Issue 8</h4>
212 <blockquote>
213 <p>Austin Group Defect 854 is applied, adding a note to the APPLICATION USAGE section that this utility is required to be
214 intrinsic.</p>
215 <p>Austin Group Defect 1122 is applied, changing the description of <i>NLSPATH .</i></p>
216 <p>Austin Group Defect 1254 is applied, updating the DESCRIPTION to account for the addition of <a href=
217 "../utilities/V3_chap02.html#tag_19_11"><i>2.11 Job Control</i></a> and adding a paragraph to RATIONALE.</p>
218 </blockquote>
219 <div class="box"><em>End of informative text.</em></div>
220 <hr>
221 <p> </p>
222 <a href="#top"><span class="topOfPage">return to top of page</span></a><br>
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