In a
Unix shell, the
full stop
The full stop (Commonwealth English), period (North American English), or full point , is a punctuation mark. It is used for several purposes, most often to mark the end of a declarative sentence (as distinguished from a question or exclamation ...
called the dot command (.) is a
command that
evaluates commands in a
computer file in the current execution context.
In
C Shell, a similar functionality is provided as the
source command,
and this name is seen in "extended" POSIX shells as well.
[
The dot command is not to be confused with a ]dot file
In computing, a hidden folder (sometimes hidden directory) or hidden file is a folder or file which filesystem utilities do not display by default when showing a directory listing. They are commonly used for storing user preferences or preservi ...
, which is a dot-prefixed hidden file or hidden directory. Nor is it to be confused with the ./scriptfile notation for running commands, which is simply a relative path pointing to the current directory (notated in Unix as a '.' character, and typically outside of the Path variable
PATH is an environment variable on Unix-like operating systems, DOS, OS/2, and Microsoft Windows, specifying a set of directories where executable programs are located. In general, each executing process or user session has its own PATH set ...
).
Arguments
The filename
A filename or file name is a name used to uniquely identify a computer file in a directory structure. Different file systems impose different restrictions on filename lengths.
A filename may (depending on the file system) include:
* name &ndas ...
is the dot command's first argument
An argument is a statement or group of statements called premises intended to determine the degree of truth or acceptability of another statement called conclusion. Arguments can be studied from three main perspectives: the logical, the dialectic ...
. When this argument does not contain a slash
Slash may refer to:
* Slash (punctuation), the "/" character
Arts and entertainment Fictional characters
* Slash (Marvel Comics)
* Slash (''Teenage Mutant Ninja Turtles'')
Music
* Harry Slash & The Slashtones, an American rock band
* Nash th ...
, the shell will search for the file in all directories defined in the PATH environment variable. Unlike normal commands which are also found in PATH, the file to source does not have to be executable
In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), instructi ...
. Otherwise the filename is considered as a simple path to the file.[
In several "extended" shells including bash,]$0 will be the $0 of the current context.
Usages
Since the execution of the source file is done in the invoking context, environment changed within apply to the current process or the current shell. This is very different from scripts run directly by shebang or as sh foo.sh, which are run in a new, separate process space
A process is a series or set of Action (philosophy), activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that p ...
, with a separate environment.
Therefore, the dot command can be used for splitting a big script into smaller pieces, potentially enabling modular design. Sourcing is also often done by the shell on session startup for user profile files like .bashrc and .profile.
Source
source is a shell-builtin command that evaluates the file following the command, as a list of commands, executed in the current context.["BASH BUILTIN COMMANDS", the Linux man page for "source" in Bash-3.0. 2004 Apr 20] Frequently the "current context" is a terminal window into which the user is typing commands during an interactive session.
The source command can be abbreviated as just a dot (.) in Bash and similar POSIX-ish shells. However, this is not acceptable in C shell, where the command first appeared.
Some Bash script
Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been used as the default login shell for most Linux distributions. Bash ...
s should be run using the source your-script syntax rather than run as an executable command, e.g., if they contain a change directory
The command, also known as (change directory), is a command-line shell command used to change the current working directory in various operating systems. It can be used in shell scripts and batch files.
Implementations
The command has b ...
(cd) command and the user intends that they be left in that directory after the script is complete, or they contain an export command and the user wants to modify the environment of the current shell. Another usage situation is when a script file does not have the "execute" permission. Passing the script filename to the desired shell will run the script in a subshell, not the current context.
Notes
References
External links
The three different uses of the dot in Unix explained
{{Unix commands
Standard Unix programs
Unix SUS2008 utilities
IBM i Qshell commands