> ## Documentation Index > Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt > Use this file to discover all available pages before exploring further. # Bash Source File The `source` command (and its POSIX-compliant equivalent, the dot operator `.`) is a shell built-in that reads and evaluates commands from a specified file directly within the current shell execution context. Unlike standard script execution, sourcing a file does not spawn a child process (subshell). ## Syntax ```bash theme={"dark"} source filename [arguments] . filename [arguments] ``` ## Execution Context and State Mutation Because the file is evaluated in the current shell environment, any state changes invoked by the file persist in the calling shell after execution completes. * **Environment Variables:** Variable assignments and `export` declarations become immediately available in the parent shell. * **Functions and Aliases:** Any functions or aliases defined in the sourced file are registered in the current shell's memory space. * **Working Directory:** Commands that modify the environment, such as `cd`, will change the working directory of the active shell session. * **Permissions:** The target file requires read (`r`) permissions, but strictly does not require execute (`x`) permissions, as the file is read as a stream of commands rather than invoked as an executable binary or script. ## Control Flow The `return` built-in can be used inside a sourced file to halt its execution early. When `return` is encountered, Bash stops reading the sourced file and returns control to the calling shell, passing back the specified exit status. This behaves exactly as it does when terminating a shell function. ## Path Resolution When a file is sourced, Bash uses specific rules to locate the file: 1. If the `filename` contains a directory path (e.g., `./script.sh` or `/etc/script.sh`), Bash reads that exact file. 2. If the `filename` does not contain a slash (`/`), Bash checks the `sourcepath` shell option (`shopt -s sourcepath`), which is enabled by default. If `sourcepath` is enabled, Bash searches the directories defined in the `$PATH` environment variable. 3. If the file is not found in `$PATH`, default Bash falls back to searching the current working directory. However, if Bash is operating in POSIX mode (`set -o posix` or invoked as `sh`), this fallback is disabled, and the current directory is not searched unless it is explicitly included in `$PATH`. ## Positional Parameters The `source` command handles positional parameters (`$1`, `$2`, `$@`, etc.) dynamically based on how it is invoked: * **With Arguments:** If arguments are appended to the `source` command, they temporarily replace the calling shell's positional parameters for the duration of the sourced file's execution. Once the file finishes evaluating, the calling shell's original positional parameters are restored. * **Without Arguments:** If no arguments are provided, the sourced file inherits the current positional parameters of the calling shell. ## Exit Status and Error Handling The return value (`$?`) of the `source` command is the exit status of the last command executed within the sourced file. If the file is empty or no commands are executed, the exit status is `0`. If execution is halted via the `return` built-in, the exit status is the argument passed to `return`. If the specified file cannot be found or read, `source` returns a non-zero exit status (typically `1`). In default Bash, this will cause a non-interactive shell to exit only if the `errexit` (`set -e`) option is enabled. However, in POSIX mode, failing to find the sourced file is a fatal error that immediately aborts a non-interactive shell, regardless of whether the `errexit` option is enabled.

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