The ‘dot space filename’ command doing in bash

bashexport

When using bash shell, I sometimes keep environment variables in a text file which I copy/paste the content of, eg exports.txt:

export FOO=bar
export FIZZ=buzz

Someone showed me instead of copy/paste, I could type in the terminal

. exports.txt

which would have the same effect as copy/paste.

What is the mechanism by which this 'dot space filename' command works? It's hard to think of search terms for it.

I want to understand what is happening and the more general details of what this one-liner is doing.

Best Answer

The . ("dot") command is a synonym/shortcut for the shell's built-in source command.

It causes the named shell script to be read in and executed within the current shell context (rather than a subshell). This allows the sourced script to modify the environment of the calling shell, such as setting variables and defining shell functions and aliases.

Related Solutions

Macos – initialize the environment when the shell loads

In the general case you can use ~/.profile

Also note (from the bash manpage):

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable.

and:

When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files exist. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of /etc/bash.bashrc and ~/.bashrc.

For a more complete question/answer, see:

Linux – Where should I export an environment variable so that all combinations of bash/dash, interactive/non-interactive, login/non-login, will pick it up

Shell invocation is a bit of a complicated thing. The bash and dash man pages has INVOCATION sections about this.

In summary they says (there is more detail in the man page, you should read it):

When bash is                   | it reads
-------------------------------|----------
login shell                    | /etc/profile and then the first of ~/.bash_profile, ~/.bash_login or ~/.profile that exists.
                               |
interactive non-login shell    | /etc/bash.bashrc then ~/.bashrc
                               |
non-interactive shell          | The contents of $BASH_ENV (if it exists)
                               |
interactive (as "sh")          | The contents of $ENV (if it exists)

When dash is                   | it reads
-------------------------------|---------
login shell                    | /etc/profile then .profile
                               |
interactive shell              | The contents of ENV (it it exists, can be set in .profile as well as in initial environment)

I don't know about other shells offhand as I never use any of them. Your best bet might be to set a couple environment variables to point at the common location script and manually source that (when appropriate) in the couple of cases that doesn't cover.

Best Answer

Related Solutions

Macos – initialize the environment when the shell loads

Linux – Where should I export an environment variable so that all combinations of bash/dash, interactive/non-interactive, login/non-login, will pick it up

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