$ whatis source
source: nothing appropriate.
$ man source
No manual entry for source
$ source
bash: source: filename argument required
source: usage: source filename [arguments]
It exists, and it is runnable. Why isn't there any documentation about it in Ubuntu? What does it do? How can I install documentation about it?
12 Answers
source is a bash shell built-in command that executes the content of the file passed as argument, in the current shell. It has a synonym in . (period).
Syntax
. filename [arguments] source filename [arguments]
Be careful! ./ and source are not quite the same.
./scriptruns the script as an executable file, launching a new shell to run itsource scriptreads and executes commands from filename in the current shell environment
Note: ./script is not . script, but . script == source script
It is useful to know the 'type' command:
> type source
source is a shell builtin
whenever something is a shell builtin it is time to do man bash.
. (a period) is a bash shell built-in command that executes the commands from a file passed as argument, in the current shell. 'source' is a synonym for '.'.
From Bash man page:
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell
environment and return the exit status of the last command exe‐
cuted from filename. If filename does not contain a slash, file
names in PATH are used to find the directory containing file‐
name. The file searched for in PATH need not be executable.
When bash is not in posix mode, the current directory is
searched if no file is found in PATH. If the sourcepath option
to the shopt builtin command is turned off, the PATH is not
searched. If any arguments are supplied, they become the posi‐
tional parameters when filename is executed. Otherwise the
positional parameters are unchanged. The return status is the
status of the last command exited within the script (0 if no
commands are executed), and false if filename is not found or
cannot be read.
'source' is the long version of '.' command. On the bash prompt one can do:
source ~/.bashrc
to reload your (changed?) bash setting for current running bash.
Short version would be:
. ~/.bashrc
The man page:
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell environment and
return the exit status of the last command executed from filename. If
filename does not contain a slash, file names in PATH are used to find the
directory containing filename. The file searched for in PATH need not be
executable. When bash is not in posix mode, the current directory is
searched if no file is found in PATH. If the sourcepath option to the shopt
builtin command is turned off, the PATH is not searched. If any arguments
are supplied, they become the positional parameters when filename is
executed. Otherwise the positional parameters are unchanged. The return
status is the status of the last command exited within the script (0 if no
commands are executed), and false if filename is not found or cannot be
read.
source command executes the provided script (executable permission is not mandatory) in the current shell environment, while ./ executes the provided executable script in a new shell.
source command do have a synonym . filename.
To make it more clear, have a look at the following script, which sets the alias.
make_alias
#! /bin/bash
alias myproject='cd ~/Documents/Projects/2015/NewProject'
Now we have two choices to execute this script. But with only one option, the desired alias for current shell can be created among these two options.
Option 1: ./make_alias
Make script executable first.
chmod +x make_alias
Execute
./make_alias
Verify
alias
Output
**nothing**
Whoops! Alias is gone with the new shell.
Let's go with the second option.
