On Tue, 22 Mar 2011, Dennis Benzinger wrote:
Hi!
I have a log file with timestamps and messages:
01:00 x
02:00 y
03:00 z
To compare the time elapsed between two events I want to prefix each
line with the timestamp of the previous time. I tried to use
%s/^/\=matchstr(getline(line(".")-1), "\\d\\{2}:\\d\\{2} ")
but somehow the first match is prepended to every line:
01:00 x
01:00 02:00 y
01:00 03:00 z
By the time the expression is evaluated, you've prepended the timestamp
from two lines prior to the prior line.
So, using your example:
line(1)=="01:00 x"
line(2)=="02:00 y"
line(3)=="03:00 z"
On line (1) the matchstr() doesn't prepend anything, since nonexistent
line(0) doesn't match the timestamp pattern.
On line (2) the matchstr() prepends line(1)'s "01:00 ".
When it reaches line(3), line(2) == "01:00 02:00 y". So, it grabs the
"01:00 " again.
I'm not sure if there's a way to specify that a range should be
reversed. But, you could also substitute it in such a way that it no
longer matches the pattern:
:%s/^/\='_GUARD_PATTERN_'.matchstr(getline(line(".")-1),
'\%(_GUARD_PATTERN_\)\@<!\d\{2}:\d\{2} ')
:%s/_GUARD_PATTERN_//
--
Best,
Ben
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