Bash - Here Documents
Language - Here Document in Bash.
Here document in Bash is implemented through redirection. A redirection instructs the shell to read input from the current source until a line containing only word (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command.
FirstWorldDelimiter not quoted
foo="foo" cat <<-HereDoc my Variable is $foo HereDoc
my Variable is foo
foo="foo" cat <<-"HereDoc" my Variable is $foo HereDoc
my Variable is $foo
The format of here-documents is:
<<[-]wordDelimiter here-document wordDelimiter
- « is the redirection operator
- - (optional) is used then all leading tab characters are stripped from input lines and the line containing delimiter. This allows here-documents within shell scripts to be indented in a natural fashion.
- wordDelimiter and wordDelimiter delimit the content of the here-document
Bash variant: The word is expanded and supplied to the command on its standard input.
is performed on the first WordDelimiter.
If the first wordDelimiter is:
- quoted, the lines in the here-document are not expanded.
- unquoted, all lines of the here-document are subjected to :
- and arithmetic expansion.
In the latter case, the character sequence \<newline> is ignored, and \ must be used to quote the characters \, $, and ‘.
The second WorldDelimiter is generally the result of quote removal on the first WordDelimiter.