CST8177 – Linux II
bash startup files 
 Linux/Unix files 
 stty 
 

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.midterms  

.bash startup files 

.stty 


 
     

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Topics





.We customize our shell behavior by  

.setting environment variables, for example,  



     export PATH=/bin:/usr/bin:/sbin 
.setting aliases, for example  



     alias ll="ls –l" 
.setting shell options, for example,  



     shopt –s failglob or shopt –s dotglob 
.setting shell options, for example,  



     set –o noclobber 
we make these customizations permanent using bash startup files    

Configuring Bash Behavior
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.http://teaching.idallen.com/cst8207/13f/notes/210_startup_files.html 

.~/.bash_profile is sourced by your login shell when you log in 

.the things we set up here are done only once when we log in 

.export-ed variables here are inherited by subshells 

.we source ~/.bashrc here because login shells do not source it  


.~/.bashrc is sourced by each non-login subshell, interactive or not 

.here we set up things that are not inherited from the login shell 

.inside this file, at the top, we check whether it’s an interactive or non-interactive shell: 



[ -z "${PS1-}" ] && return 
.we set aliases in this file 

.we set options configured with shopt and set in this file    




Bash Startup Files
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.When a login shell starts 

1.execute  commands  from /etc/profile, if that file exists 

2.execute commands from the first of these that is readable (in order): 

1.~/.bash_profile 

2.~/.bash_login 

3.~/.profile 



.When a login shell exits 

1.read and execute commands from the file ~/.bash_logout, if it exists  




Startup File Sequence
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.When an interactive non-login shell starts 

1.execute  commands  from ~/.bashrc, if that file exists 


.The -–rcfile file option specifies that file should be used instead of ~/.bashrc  



Startup File Sequence (cont’d)
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.The system administrator can configure the default shell environment for all users 

.Configuration in /etc/profile applies to all users on the system 

.The files in /etc/skel/ are copied to newly created user accounts (can give new users a default copy of .bash_profile and .bashrc) 



System Wide Shell Configuration
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.The bash process used to execute a shell script is non-interactive 

.stdin and stdout not connected to a terminal (more details in bash manpage) 



Non-Interactive Shells
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..bash_profile is loaded once by a login shell 

..bashrc is loaded by non-login shells 

.There are cases where there never is a login shell, for example 


 ssh remote-server.com <some_command> 
.So the method we'll use in this course: 

..bash_profile does nothing except load .bashrc 

..bashrc keeps track of things that should be done only once 




.bashrc versus .bash_profile
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[ -z "${PS1-}" ] && return 
if [ "${_FIRST_SHELL-}" = "" ] ; then 
    export _FIRST_SHELL=$$ 
    export PATH="$PATH:$HOME/bin" 
    export LC_ALL=en_CA.UTF-8 
    export LANG=en_CA.UTF-8 
    # here we put things that 
    # should be done once 
fi 
# here we put things that need to be 
# done for every interactive shell 
 

.bashrc
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Contains just one line: 
 
source ./.bashrc 

.bash_profile
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.recall the effect of these control characters: 

.^Z suspend the current foreground process 

.^C terminate the current foreground process 

.^D end of file character 

.^U kill character to erase the command line 


.these are actually properties of the terminal 

.they can be set with the stty command 

.stty –a  : print out the current tty settings 

.stty susp ^X :(that’s a caret ^, shift-6 on my keyboard, followed by capital X) means set the susp character to CTRL-X instead of CTRL-Z 


 

New Commands: stty
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.if you accidentally dump the contents of a binary file to your screen, and all the control characters reconfigure your terminal on you, you can reset it to sane values with 


      stty sane 

stty (cont’d)
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