". filename" can't find file when run from /bin/sh, works from /bin/bash; why?

Question

My simple script is like this:

#!/bin/sh


DEF=.file_name_with_a_leading_dot.sh

. ${DEF}

Notice the /bin/sh on the top line. When I run that simple script I get an error that the file isn't found. But, if I change that top line to #!/bin/bash then the script finds that file in the current directory just fine.

But, On my Ubuntu linux laptop I see that /bin/sh is a symlink to /bin/bash . So, why does my script behave differently?

Also, I can run the script like this:

/bin/bash ./script.sh

And it's OK.

So, what am I missing?

Answer 1

From the Manpage:

. 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.

So, it seems that the shebang #!/bin/sh sets your bash to posix mode. In this mode, only PATH is evaluated, not the current directory.