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96 lines
4.3 KiB
HTML
96 lines
4.3 KiB
HTML
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<link rel="stylesheet" href="../../../../../style.css">
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<base target="_parent">
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<title data-trilium-title>Bash startup modes</title>
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<div class="content">
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<h1 data-trilium-h1>Bash startup modes</h1>
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<div class="ck-content">
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<h3>Login shell</h3>
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<p>As a "login shell", Bash reads and sets (executes) the user's profile
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from /etc/profile and one of ~/.bash_profile, ~/.bash_login, or ~/.profile
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(in that order, using the first one that's readable!).</p>
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<p>When a login shell exits, Bash reads and executes commands from the file
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~/.bash_logout, if it exists.</p>
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<p>Why an extra login shell mode? There are many actions and variable sets
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that only make sense for the initial user login. That's why all UNIX® shells
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have (should have) a "login" mode.</p>
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<p><em><strong>Methods to start Bash as a login shell:</strong></em>
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</p>
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<ul>
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<li>the first character of argv[0] is - (a hyphen): traditional UNIX® shells
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start from the login binary</li>
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<li>Bash is started with the -l option</li>
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<li>Bash is started with the --login option</li>
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</ul>
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<p><em><strong>Methods to test for login shell mode:</strong></em>
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</p>
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<ul>
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<li>the shell option <a href="http://wiki.bash-hackers.org/internals/shell_options#login_shell">login_shell</a> is
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set</li>
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</ul>
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<p><em><strong>Related switches:</strong></em>
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</p>
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<ul>
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<li>--noprofile disables reading of all profile files</li>
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</ul>
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<h3>Interactive shell</h3>
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<p>When Bash starts as an interactive non-login shell, it reads and executes
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commands from ~/.bashrc. This file should contain, for example, aliases,
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since they need to be defined in every shell as they're not inherited from
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the parent shell.</p>
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<p>The feature to have a system-wide /etc/bash.bashrc or a similar system-wide
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rc-file is specific to vendors and distributors that ship <em>their own, patched variant of Bash</em>.
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The classic way to have a system-wide rc file is to source /etc/bashrc
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from every user's ~/.bashrc.</p>
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<p><em><strong>Methods to test for interactive-shell mode:</strong></em>
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</p>
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<ul>
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<li>the special parameter $- contains the letter i (lowercase I)</li>
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</ul>
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<p><em><strong>Related switches:</strong></em>
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</p>
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<ul>
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<li>-i forces the interactive mode</li>
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<li>--norc disables reading of the startup files (e.g. /etc/bash.bashrc if
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supported) and ~/.bashrc</li>
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<li>--rcfile defines another startup file (instead of /etc/bash.bashrc and
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~/.bashrc)</li>
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</ul>
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<h3>SH mode</h3>
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<p>When Bash starts in SH compatiblity mode, it tries to mimic the startup
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behaviour of historical versions of sh as closely as possible, while conforming
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to the POSIX® standard as well. The profile files read are /etc/profile
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and ~/.profile, if it's a login shell.</p>
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<p>If it's not a login shell, the environment variable <a href="http://wiki.bash-hackers.org/syntax/shellvars#env">ENV</a> is
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evaluated and the resulting filename is used as the name of the startup
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file.</p>
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<p>After the startup files are read, Bash enters the <a href="http://wiki.bash-hackers.org/scripting/bashbehaviour#posix_run_mode">POSIX(r) compatiblity mode (for running, not for starting!)</a>.</p>
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<p><em><strong>Bash starts in sh compatiblity mode when:</strong></em>
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</p>
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<ul>
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<li>
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<p>the base filename in argv[0] is sh (</p>
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<figure class="image">
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<img>
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</figure>
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<p> NB: /bin/sh may be linked to /bin/bash, but that doesn't mean it
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acts like /bin/bash </p>
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<figure class="image">
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<img>
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</figure>
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<p>)</p>
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</li>
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</ul>
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</div>
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</div>
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</body>
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</html> |