On 3/23/2016 12:12 PM, Ralf Friedl wrote:
Cristian Ionescu-Idbohrn wrote:
sed (GNU sed) 4.2.2 can do this:
$ printf 'foo
bar
baz' | sed r -
foo
bar
baz
or, after storing the text in a file:
$ printf 'foo
bar
baz' >/tmp/bar
$ sed r /tmp/bar
foo
bar
baz
But busybox sed can't:
$ printf 'foo
bar
baz' | busybox sed r -
sed: empty filename
$ busybox sed r /tmp/bar
sed: empty filename
$ printf '' | busybox sed 'r /tmp/bar'
<no output, although /tmp/bar size is 11 bytes>
$ busybox sed 'r /tmp/bar'
<waiting for stdin; ^D; no output>
The 'r' command is documented by GNU sed as a GNU extension. Still,
busybox sed documents the 'r' command as supported:
r [address]r file
Read contents of file and append after the contents of the
pattern space. Exactly one space must be put between r and
the
filename.
Am I misinterpreting the documentation?
From the documentation:
> The full format for invoking `sed' is:
> sed OPTIONS... [SCRIPT] [INPUTFILE...]
So in your example you invoce sed with the script "r" and the input
file "-" or "/tmp/bar". The content is not printed because it is the
argument to the "r" command, but because it is the main input file to
sed. You can avoid that by using quotes around the command and the
file name, or by omitting the space between the command and the filename.
You should also try the last two examples, where you invoke busybox
sed with quotes, with GNU sed. The behaviour is the same.
You should note that in your example when reading from a file, sed
didn't read from stdin, at least you don't mention it, although your
interpretation would mean that the filename is the argument to the "r"
command, therefor no argument is given to sed, and sed should read stdin.
You should also not that invoking the "r" command with the filename
causes the content of this file to be inserted after every line. When
reading from a pipe, the pipe is empty after the first line.
My documentation to GNU sed 4.2.2 says:
> `r FILENAME'
> As a GNU extension, this command accepts two addresses.
>
> Queue the contents of FILENAME to be read and inserted into the
> output stream at the end of the current cycle, or when the next
> input line is read. Note that if FILENAME cannot be read, it is
> treated as if it were an empty file, without any error indication.
>
> As a GNU `sed' extension, the special value `/dev/stdin' is
> supported for the file name, which reads the contents of the
> standard input.
So the main difference seems to be that GNU sed doesn't give an error
message if the file can't be read. I'm not sure why that would be a
good idea.
Also not that there is no mention of using "r -" for stdin, instead
/dev/stdin is mentioned.
On the other hand, I don't know why busybox sed needs exactly one
space between command and filename. GNU sed works with zero or more
spaces.
It looks to me that what actually happens when running "sed r" is that
it appends *no lines* to the end of each line read from stdin.
$ printf 'foo
bar
baz' | sed
Does not add a final newline
$ printf 'foo
bar
baz' | sed r
Does add a final newline
$ printf 'foo
bar
baz' | sed 'r /dev/null'
Does add a final newline
echo "blah" > -
$ printf 'foo
bar
baz' | sed 'r -'
results in
foo
blah
bar
blah
baz
blah
So it is not a special case for the filename.
I personally don't see much value in preserving the behavior of
appending nothing for a file which doesn't exist. Tools should give
errors if they can't do what you ask them to.
-Mike C.
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