Rob Landley wrote:
On Tuesday 30 June 2009 07:27:21 Maximilian Gaß wrote:
sed -n -e '1d' -e '1,/@HEADER_ENDS/p' initfini.s
Busybox sed gives no output, while GNU sed gives the expected
It's expected?
If you deleted your ending search condition before evaluating it, would you
expect your search to stop? So why do you expect your search to start when
you deleted your starting condition before evaluating it? (I believe that
according to susv3, delete ends evaluation of the sed script and jumps
immediately to the next line. So your second -e doesn't get run for line 1,
therefore it doesn't start the range.)
Looking at other kinds of addresses, if you did:
sed -n -e '1d' -e '/@HEADER_STARTS/,/@HEADER_ENDS/p' initfini.s
And line 1 was "@HEADER_STARTS", would you expect your range to start anyway?
If not, why do you expect a numerical start address to work differently?
Because /@HEADER_STARTS/ refers to a line containing @HEADER_STARTS,
while 1 refers to the first line, independent of its content.
Ok, let's look at the spec.
According to http://www.opengroup.org/onlinepubs/9699919799/toc.htm
An address is either a decimal number that counts input lines cumulatively
across files, a '$' character that addresses the last line of input, or a
context address (which consists of a BRE, as described in Regular
Expressions in sed , preceded and followed by a delimiter, usually a
<slash>).
An editing command with two addresses shall select the inclusive range from
the first pattern space that matches the first address through the next
pattern space that matches the second. (If the second address is a number
less than or equal to the line number first selected, only one line shall be
selected.) Starting at the first line following the selected range, sed shall
look again for the first address. Thereafter, the process shall be repeated.
d is "Delete the pattern space and start the next cycle".
Deleting the pattern space starts the next cycle, so the first address never
got matched, so the range didn't start...
The question here is, after line number 1 is deleted, is there no longer
a line with number 1, or does line number 2 become line number 1?
The standard you quote does not address this question, but let's assume
you were using vi with the commands ":1d" followed by ":1,$d". The first
command deletes line 1. By your reasoning, the second command should not
match, because line 1 is already deleted by the first command. Actually,
the second command deletes from what was line 2 in the original file to
the end. After both commands the entire contents of the file are
deleted. And I tried this with busybox vi.
Regards
Ralf
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