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Next
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Contents
6. Shells
Often user processes are children processes of the shell mentioned in /etc/passwd for this user. Initialization files of shells often modify path. In login, the name of the shell is preceded with '-', for example bash is called as '-bash'. This signals to the shell that it is a 'login' shell. In this case, the shell executes the 'login' initialization files. Otherwise some lighter initialization is performed. Additionally, the shell checks if it is interactive - are the commands coming from file or interactive tty. This modifies the shell initialization so that a non-interactive non-login shell is initialized very lightly - bash do not execute any initialization file in this case!
6.1 bash
As a normal login shell, bash 'sources' system-wide file /etc/profile, where the system environment and path can be set for bash users. However, it is not run when the system interprets the shell as non-interactive. The most important case is in rsh, where remote command is executed in the neighboring machine. The /etc/profile is not run and the path is inherited from rsh daemon. bash receives command line arguments -login and -i that can be used to set the shell as a login shell or interactive shell respectively. The user can overwrite values set in /etc/profile by creating a file ~/.bash_profile, ~/.bash_login or ~/.profile. Note that just the first one of these is executed thus differing of the logic of csh initialization. ~/.bash_login is not executed specially for login shells and if .bash_profile exists, it is not executed at all! If bash is used with name sh instead of the name bash, it emulates original Bourne shell initialization: it sources just files /etc/profile and ~/.profile and just for login shells.
6.2 tcsh
As a login shell tcsh executes the following files in this order:
tcsh can be compiled to execute login scripts before cshrc scripts. Beware! Non-interactive shells execute just the *cshrc scripts. *login scripts can be used to set the path just once in the login.
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This document, LDP HOWTO-INDEX, is copyrighted (c) 1995 - 2002 by Tim Bynum, Guylhem Aznar, Joshua Drake and Greg Ferguson. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is available at http://www.gnu.org/copyleft/fdl.html. If you have questions, please contact the LDP.
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