I read a file:
local logfile = io.open("log.txt", "r")
data = logfile:read("*a")
print(data)
output:
...
"(\.)\n(\w)", r"\1 \2"
"\n[^\t]", "", x, re.S
...
Yes, logfile looks awful as it's full of various commands
How can I call gsub
and remove i.e. "(\.)\n(\w)", r"\1 \2"
line from data variable?
Below snippet, does not work:
s='"(\.)\n(\w)", r"\1 \2"'
data=data:gsub(s, '')
I guess some escaping needs to be done. Any easy solution?
Update:
local data = [["(\.)\n(\w)", r"\1 \2"
"\n[^\t]", "", x, re.S]]
local s = [["(\.)\n(\w)", r"\1 \2"]]
local function esc(x)
return (x:gsub('%%', '%%%%')
:gsub('^%^', '%%^')
:gsub('%$$', '%%$')
:gsub('%(', '%%(')
:gsub('%)', '%%)')
:gsub('%.', '%%.')
:gsub('%[', '%%[')
:gsub('%]', '%%]')
:gsub('%*', '%%*')
:gsub('%+', '%%+')
:gsub('%-', '%%-')
:gsub('%?', '%%?'))
end
print(data:gsub(esc(s), ''))
This seems to works fine, only that I need to escape, escape character %
, as it wont work if %
is in matched string. I tried :gsub('%%', '%%%%')
or :gsub('\%', '\%\%')
but it doesn't work.
Update 2:
OK, %
can be escaped this way if set first in above "table" which I just corrected
:terrible experience:
Update 3:
Escaping of ^
and $
As stated in Lua manual (5.1, 5.2, 5.3)
A caret
^
at the beginning of a pattern anchors the match at the beginning of the subject string. A$
at the end of a pattern anchors the match at the end of the subject string. At other positions,^
and$
have no special meaning and represent themselves.
So a better idea would be to escape ^
and $
only when they are found (respectively) and the beginning or the end of the string.
Lua 5.1 - 5.2+ incompatibilities
string.gsub
now raises an error if the replacement string contains a%
followed by a character other than the permitted%
or digit.
There is no need to double every %
in the replacement string. See lua-users.
According to Programming in Lua:
The character `%´ works as an escape for those magic characters. So, '%.' matches a dot; '%%' matches the character `%´ itself. You can use the escape `%´ not only for the magic characters, but also for all other non-alphanumeric characters. When in doubt, play safe and put an escape.
Doesn't this mean that you can simply put %
in front of every non alphanumeric character and be fine. This would also be future proof (in the case that new special characters are introduced). Like this:
function escape_pattern(text)
return text:gsub("([^%w])", "%%%1")
end
It worked for me on Lua 5.3.2 (only rudimentary testing was performed). Not sure if it will work with older versions.