I'm just going through this post and having trouble understanding the code. Could you please explain the rindex function for me? I'm still learning..
'man nawk' yields:
Code:
match(s,ere)
Return the position, in characters, numbering from 1,
in string s where the extended regular expression ere
occurs, or zero if it does not occur at all. RSTART
will be set to the starting position (which is the
same as the returned value), zero if no match is
found; RLENGTH will be set to the length of the
matched string, -1 if no match is found.
Code:
function rindex(str,c)
{
# pass in the string to search (str) and a character to search for (c).
# function will return either a position of 'c' in string 'str' OR '0' if 'c' isn't in
# 'str'. The regex passed to 'match' goes like this:
# "\\" - literal '\' - have to escape it with '\' to preserve the meaning
# followed by char 'c' - resulting in '\c' - need to escape in case 'c' is one
# of the regex chars, e.g. '(', ')', '|' etc
# "[^" - anything BUT the following chars or ranges
# followed by char 'c'
# "]*$" - closing the char list/range - char list repeated 0 or more times (*)
# anchored to the end of the line ($).
#
# If 'match' found a passed in char, its position will be stored in the
# interval var RSTART - RSTART will be retirned
# If 'match didn't find a passeed in char, 'match' itself will return '0' -
# therefore a value of '0' will be retuned by the function.
#
# E.g. match("a|b|c|d", "\|[^|]*$")
# Look into the 'match(s,re) description above for more info.
#
return match(str,"\\" c "[^" c "]*$")? RSTART : 0
}
Quote:
Originally Posted by King Kalyan
Also, why did you use rindex function and not the following. I'm just curious to know and want to improve the way I look at problems.
Code:
idx=substr($4, 2, 17)
Thanks in advance!
'cause, I don't like 'magic numbers' and making unnecessary assumptions of the data format IF I can avoid it. E.g., what would happen if we could not guaranteed that the number of minutes/hours was always a TWO digit number: '05' vs '5'. Your '17' would not fly. Whereas looking for the LAST ':' would.
It looked to me like that assuming the leading '[' will always be in the field is safe enough for my taste. On the other hand, if I can avoid counting characters (17) and can identify a 'pattern' and use it to derive what I need, I'd always take this road.
Just my $.02
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