View source for Bash Concepts

=Internal=

* [[bash#Subjects|bash]]

=Login Shell=

A login shell is a shell whose first character of its argument zero is a -, or it was started with the <tt>--login</tt> option.

=Interactive Shell=

An interactive shell is a shell started:
* without the <tt>-c</tt> option
* without non-option arguments
* with the <tt>-i</tt> option

The interactive shell's standard input and error are both connected to terminals.

<tt>$-</tt> includes i if the shell is interactive,  allowing a script or a startup file to test this state.

=Non-interactive Shell=

A shell started with <tt>-c</tt> option.

=bash Startup Files=

When bash is invoked as an ''interactive'' login shell, or as a ''non-interactive shell with the <tt>--login</tt> option'', it first executes commands from <tt>/etc/profile</tt>, if exists. 

Them it looks for <tt>~/.bash_profile</tt>, <tt>~/.bash_login</tt> and <tt>~/.profile</tt> in that order. It executes commands from the first one that exists and is readable. The <tt>--noprofile</tt> option may be used when the shell is started to inhibit this behavior.

When a login shell exits, bash executes commands from <tt>~/.bash_logout</tt>, if it exists.

When an ''interactive'' shell that is not a login shell is started, bash executes commands from <tt>~/.bashrc</tt>, if it exists. This may be inhibited by using the <tt>--norc</tt> option. The <tt>--rcfile</tt> file option will force bash to execute commands from the specified file instead of <tt>~/.bashrc</tt>.

When bash is started in ''non-interactive mode'', to run a shell script, for example, it looks for the variable <tt>BASH_ENV</tt> in the  environment, expands  its value if it appears there, and uses the expanded value as the name of a file execute. Bash behaves  as if the following command were executed:
<pre>
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
</pre>

but the value of the PATH variable is not used to search for the file name.

If any of the files exist but cannot be read, bash reports an error.

=Variables=

{{Internal|bash Variables|bash Variables}}

=bash Environment Variables=

<blockquote style="background-color: #f9f9f9; border: solid thin lightgrey;">
:[[bash Environment Variables]]
</blockquote>

=Globbing=

Bash cannot recognize regular expressions but it can do ''filename expansion''. The process is also known as ''globbing''. The process recognizes and expands ''wild cards''. Globbing interprets the following characters:

<tt>*</tt> (the wild card). The wild card matches every name in a given directory. Strings containing * will not match filenames that start with a dot.

<tt>?</tt> The ? character serves as a single-character "wild card" for filename expansion.

character lists in square brackets

<tt>^</tt> negates the sense of match for the above.

=Command Substitution=

{{Internal|bash Command Substitution|Command Substitution}}

=Metacharacters=

==Single Quotes==

Enclosing a string in single quotes tells the shell NOT to interpret other shell metacharacters in the text between quotes.