A set of dynamic variables that can affect the running processes.

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364
votes
8answers
675k views

How to correctly add a path to PATH?

I'm wondering where a new path has to be added to the PATH environment variable. I know this can be accomplished by editing .bashrc (for example), but it's not clear how to do this. This way: export ...
127
votes
3answers
75k views

What does “LC_ALL=C” do?

What does the C value for LC_ALL do in Unix-like systems? I know that it forces the same locale for all aspects but what does C do?
90
votes
2answers
11k views

VISUAL vs EDITOR what's the difference?

I generally set both VISUAL and EDITOR environment variables to the same thing, but what's the difference? Why would I set them differently? When developing apps, why should I choose to look at VISUAL ...
74
votes
3answers
258k views

How to permanently set environmental variables

My variables are LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib ORACLE_HOME=/usr/lib/oracle/11.2/client64 How to save these variables permanently ?
71
votes
5answers
197k views

How do I set a user environment variable? (permanently, not session)

This is irritating me. I seen several suggestions (all using different files and syntax) and none of them worked. How do I set an environment variable for a specific user? I am on debian squeeze. ...
67
votes
4answers
8k views

Is there a “.bashrc” equivalent file read by all shells?

Is ~/.bashrc the only place to specify user specific environment variables, aliases, modifications to PATH variable, etc? I ask because it seems that ~/.bashrc seems to be bash-only, but other ...
61
votes
3answers
11k views

$VAR vs ${VAR} and to quote or not to quote

I can write VAR=$VAR1 VAR=${VAR1} VAR="$VAR1" VAR="${VAR1}" the end result to me all seems about the same. Why should I write one or the other? are any of these not portable/POSIX?
54
votes
4answers
36k views

Why is `while IFS= read` used so often, instead of `IFS=; while read..`?

It seems that normal practice would put the setting of IFS outside the while loop in order to not repeat setting it for each iteration... Is this just a habitual "monkey see, monkey do" style, as it ...
46
votes
4answers
3k views

Is there ever a good reason to run sudo su?

To launch a root shell on machines where the root account is disabled, you can run one of: sudo -i : run an interactive login shell (reads /root/.bashrc and /root/.profile) sudo -s : run a non-login ...
44
votes
3answers
17k views

How does /usr/bin/env know which program to use?

When I use the shebang #!/usr/bin/env python to run a script, how does the system know which python to use? if I look for a python bin path in the environment variables I find nothing. env | grep -i ...
41
votes
9answers
77k views

How can I run a cron command with existing environmental variables?

How can I run a cron command with existing environmental variables? If I am at a shell prompt I can type echo $ORACLE_HOME and get a path. This is one of my environmental variables that gets set in ...
41
votes
4answers
2k views

What exactly is an environment variable?

I know that VARIABLE=value creates an environment variable, and export VARIABLE=value makes it available to processes created by the current shell. env shows the current environment variables, but ...
40
votes
3answers
76k views

How do I set an environment variable on the command line and have it appear in commands?

If I run export TEST=foo echo $TEST It outputs foo. If I run TEST=foo echo $TEST It does not. How can I get this functionality without using export or a script?
38
votes
7answers
14k views

How to determine where an environment variable came from

I have a linux instance that I set up some time ago. When I fire it up and log in as root there are some environment variables that I set up but I can't remember or find where they came from. I've ...
38
votes
3answers
18k views

How to run a program in a clean environment in bash?

I want to run a program in an empty environment (i.e. with no envariables set). How to do this in bash?
37
votes
3answers
41k views

How do I change the default text editor in the Debian (squeeze) distro

"Joe's own editor" does not come naturally to me. How do I change to using nano or vim? I've tried export EDITOR=nano but it doesn't seem to be respected. I'd like visudo to respect this as well.
37
votes
3answers
25k views

What is the difference between ~/.profile, ~/.bashrc, ~/.bash_profile, ~/.gnomerc, /etc/bash_bashrc, /etc/screenrc …?

Answers to the questions on SO and askubuntu, along with poking through (and reading headers of) $HOME and /etc/, indicate a number of files that can be used to set environment variables, including: ...
32
votes
5answers
7k views

why is setting a variable before a command legal in bash?

I've just encountered several answers such as to parsing a delimited text file... that use the construct: while IFS=, read xx yy zz;do echo $xx $yy $zz done < input_file where the IFS ...
28
votes
6answers
13k views

How to print only defined variables (shell and/or environment variables) in bash

The bash builtin command set, if invoked without arguments, will print all shell and environment variables, but also all defined functions. This makes the output unusable for humans and difficult to ...
27
votes
2answers
1k views

Does ~ always equal $HOME

I know this has probably been asked before, but I couldn't find it with Google. Given Linux Kernel No configurations that change $HOME bash Will ~ == $HOME be true?
27
votes
3answers
27k views

How to make unix service see environment variables?

I have set my environment variable using /etc/profile: export VAR=/home/userhome Then if I do echo $VAR it shows /home/userhome But when I put reference to this variable into the ...
26
votes
2answers
45k views

Refresh env variables after editing bashrc file

I frequently edited the .bashrc file to export new environment variables. Rather than close the console and start a new one to refresh the env variables, is there a convenient way to refresh?
26
votes
3answers
5k views

If processes inherit the parent's environment, why do we need export?

I read here that the purpose of export in a shell is to make the variable available to sub-processes started from the shell. However, I have also read here and here that "Processes inherit their ...
23
votes
2answers
8k views

How do I start all shell sessions in a directory other than $HOME?

When I open my non-login shell in Ubuntu, my present working directory is /home/user_name (my $HOME environment variable), but I want to change this such that when I start my terminal I am in some ...
22
votes
3answers
17k views

.bash_profile not sourced when running su

I have a user, say user1, which has modifications to its .bash_profile, one of them changing the PATH, e.g.: export PATH=/some/place:$PATH. This change works fine if I log on as user1 or do a su - ...
22
votes
1answer
8k views

Difference between environment variables and exported environment variables in bash

Bash seems to differentiate between variables which have been exported and those which have not. example: $ FOO=BAR $ env | grep FOO $ set | grep FOO FOO=BAR set sees the variable but env does ...
21
votes
3answers
2k views

Show PATH in a human-readable way

I want to show my PATH environment variable in a more human-readable way. $ echo $PATH ...
21
votes
4answers
9k views

Why do I have to re-set env vars in tmux when I re-attach?

I mainly work on a mac and ssh/tmux attach to a Linux machine to do my work. I have ssh-agent running on the Linux machine. I have set -g update-environment "SSH_AUTH_SOCK SSH_ASKPASS WINDOWID ...
20
votes
2answers
2k views

What's the best distro/shell-agnostic way to set environment variables?

The question says it all. I currently use Arch Linux and the zsh, but I'd like a solution that (at minimum) works both on VTs and in xterms and also (hopefully, preferably) will continue to work if I ...
20
votes
1answer
4k views

Shebang line with `#!/usr/bin/env command --argument` fails on Linux

I've got a simple script: #!/usr/bin/env ruby --verbose # script.rb puts "hi" On my OSX box, it runs fine: osx% ./script.rb hi However, on my linux box, it throws an error linux% ./script.rb ...
20
votes
6answers
28k views

How can I run a script immediately after connecting via SSH?

I started to ask this question but answered it while I had it open. I'm going to post this question, follow it up with my solution and leave it open to other potential solutions. <backstory> ...
19
votes
8answers
1k views

How do I source another process's environment variables?

If I examine /proc/1/environ I can see a null-byte-delimited string of process 1's environment variables. I'd like to bring these variables into my current environment. Is there an easy way to do ...
19
votes
4answers
25k views

What scopes can shell variables have?

I just ran into a problem that shows me I'm not clear on the scope of shell variables. I was trying to use bundle install, which is a Ruby command that uses the value of $GEM_HOME to do its work. I ...
19
votes
3answers
17k views

How to read environment variables of a process

Linux's /proc/<pid>/environ does not update (as I understand it, the file contain the initial environment of the process). How can I read a process's current environment?
19
votes
3answers
3k views

Using variables to store terminal color codes for PS1?

In my .bashrc, I use ANSI terminal color codes to colorize various bits. It looks like this: PS1='\u@\h:\w\[\033[33m\]$(virtual_env)\[\033[32m\]$(git_branch)\[\033[0m\]$ ' where virtual_env and ...
19
votes
1answer
1k views

Why does exporting vim as EDITOR in zsh disable keyboard shortcuts?

My .zshrc looks like this: export EDITOR="/usr/bin/vim" Now when I open a terminal and enter a keyboard shortcut like ctrla to go to the beginning of the line, it doesn't work. Instead, the string ...
18
votes
2answers
17k views

Who sets $USER and $USERNAME environment variables?

Also, will these variables always match currently logged-in username (they do on my Debian system)? Can I assume their availability in other Unix(-like) systems? I'm also curious why one would use ...
17
votes
1answer
331 views

Is there a difference between prepending a name-value-pair to a command and using env in bash?

Let's say I invoke A=B command and env A=B command in bash. Is there any situation where there might be a difference between both invokations?
16
votes
3answers
1k views

Issue an error when using empty shell variables

Sometimes I use, $PROJECT_HOME/* to delete all files in the project. When the environment variable, PROJECT_HOME is not set (because I did su and the new user doesn't have this environment variable ...
16
votes
3answers
14k views

using export in .bashrc

I have noticed in my .bashrc, that some lines have export in front, such as export HISTTIMEFORMAT="%b-%d %H:%M " ... export MYSQL_HISTFILE="/root/.mysql_history" whereas other have not, such as ...
16
votes
1answer
19k views

How can I make variables “exported” in a bash script stick around?

I have multiple Amazon EC2 accounts and want to quickly be able to switch variables, such as $EC2_HOME, using a script. I have have a shell script set up like this: #!/bin/sh export ...
16
votes
6answers
13k views

Why are PATH variables different when running via sudo and su?

On my fedora VM, when running with my user account I have /usr/local/bin in my path: [justin@justin-fedora12 ~]$ env | grep PATH ...
15
votes
5answers
9k views

How is sudo set to not change $HOME in Ubuntu and how to disable this behavior?

On Ubuntu 12.04, when I sudo -s the $HOME variable is not changed, so if my regular user is regularuser, the situation goes like this: $ cd $ pwd /home/regularuser $ sudo -s # cd # pwd ...
15
votes
2answers
7k views

In zsh how can I list all the environment variables?

I want to get a list of all environment variables (shell variables? exported variables?) and their values at a given time, in zsh. What is the proper way to do this?
15
votes
3answers
5k views

The way to use `/usr/bin/env sed -f ` in shebang?

Typing /usr/bin/env sed -f in terminal works. But if use it as a shebang, #!/usr/bin/env sed -f s/a/b/ The script will be fail to execute: /usr/bin/env: sed -f: No such file or directory I ...
15
votes
1answer
3k views

change environment of a running process

How might it be possible to alter some variable in the env of an already running process, for example through /proc/PID/environ? That "file" is read-only. Need to change or unset the DISPLAY variable ...
14
votes
5answers
26k views

Script to change current directory (cd, pwd)

I want to run a script to simply change the current working directory: #!/bin/bash cd web/www/project But, after I run it, the current pwd remains unchanged! How can I do that?
14
votes
2answers
14k views

How to reset a shell environment?

This issue has been bugging me for a while, and although I've thought I've found my answer through EnvWatcher, unfortunately it only works on Bash. And I use zsh. I would like to replicate the things ...
14
votes
4answers
1k views

keep duplicates out of $PATH on source [duplicate]

I have the following code that's source-d by my .shellrc PATH="${PATH}:${HOME}/perl5/bin" PATH="${PATH}:${HOME}/.bin" export PATH but if I make changes to other code and then source this file, my ...
13
votes
1answer
26k views

how to set environment variables from a shell script? [duplicate]

I'm trying to set environment variable through a shell script. Here is the script with various techniques: #!/bin/sh echo "export SOMEPATH=/root/some" >> /root/.bash_profile echo "export ...