What does source do?

Question

$ 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, it is runnable, why there is no documentation about it in ubuntu? What does it do? How can I install documentation about it?

Answer 1

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]

Answer 2

. (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.

Answer 3

'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.

edit: can't get the above to format in a nice way, sorry

Answer 4

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.

Answer 5

This is a shell built-in command, read the manual for your shell.

which source

man bash