I'm familiar with this syntax:
cmd1 << EOF | cmd2
text
EOF
but just discovered that bash allows me to write:
cmd1 << EOF |
text
EOF
cmd2
(the heredoc is used as input to cmd1, and the output of cmd1 is piped to cmd2). This seems like a very odd syntax. Is it portable?
Yes, the POSIX standard allows this. According to the 2008 version:
The here-document shall be treated as a single word that begins after the next
<newline>
and continues until there is a line containing only the delimiter and a<newline>
, with no<blank>
characters in between. Then the next here-document starts, if there is one.
And includes this example of multiple "here-documents" in the same line:
cat <<eof1; cat <<eof2
Hi,
eof1
Helene.
eof2
So there is no problem doing redirections or pipes. Your example is similar to something like this:
cat file |
cmd
And the shell grammar (further down on the linked page) includes these definitions:
pipe_sequence : command
| pipe_sequence '|' linebreak command
newline_list : NEWLINE
| newline_list NEWLINE
;
linebreak : newline_list
| /* empty */
So a pipe symbol can be followed by an end-of-line and still be considered part of a pipeline.
Yes it's in the POSIX shell grammar. You can also have more than one here-doc for the same command (some other examples use two cat
invocations, but this works as well):
cat <<EOF1 <<EOF2
first here-doc
EOF1
second here-doc
EOF2
This is contrived (using 2 here-docs for stdin), but if you think of providing input for different file descriptors it immediately makes sense.
There's also the possibility to drop the cat
entirely . Why not make the here-document directly available to cmd
:
cmd << EOF
input
here
EOF
Hmm, I suppose yes, according to the test in bash in POSIX mode:
$ bash --posix
$ cat <<EOF |
> ahoj
> nazdar
> EOF
> sed 's/a/b/'
bhoj
nbzdar
Hi, check this, for example
#!/bin/sh
( base32 -d | base64 -d )<<ENDOFTEXT
KNDWW42DNNSHS5ZXPJCG4MSVM5MVQVT2JFCTK3DELBFDCY2IIJYGE2JUJNHWS22LINVHQMCMNVFD
CWJQIIZVUV2JOVNEOVJLINTW6PIK
ENDOFTEXT
regards
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