On 2/8/2008 9:19 AM, Luuk wrote:
> Ed Morton schreef:
>
>>On 2/8/2008 6:50 AM, Luuk wrote:
<snip>
>>>could someone explain the '1' in "$ awk 'gsub(/.*\(....|\)$/,"")1'
file" ?
>>
>>It makes sure that even if the input record is empty (in which case
gsub() will
>>return 0) the eventual condition being tested by awk is
non-zero/non-null so
>>that printing the current record occurs even in that case.
>>
>>The operator used to combine the result of the gsub() with the "1" is
>>string-concatenation so you can put anything after the gsub() to get a
non-null
>>resultant string, even zero (to get the string "00") or the null string
(to get
>>the string "0" as opposed to the number zero).
>>
>>
>>>awk does not seem to do anything with it...
>>>or is it just a typo?
>>
>>No. Look:
>>
>>$ cat file
>>a
>>
>>c
>>$ awk 'sub(/./,NR)' file
>>1
>>3
>>$ awk 'sub(/./,NR)1' file
>>1
>>
>>3
>>
>>
>>>but awk also does not complain when i type:
>>>$ awk 'gsub(/.*\(....|\)$/,"")g' file
>>
>>Right. In that case it evaluates the unassigned variable "g" to the null
string
>>"" which is string-concatenated with the zero result of sub() to give a
non-null
>>"0" string:
>>
>>$ awk 'sub(/./,NR)g' file
>>1
>>
>>3
>>
>>Regards,
>>
>> Ed.
>>
>
>
>
> i must have skipped that part of the man-page....
I think it's in the fine-print at the bottom under "What???" :-).
> normally i use to do:
> awk '{ sub(/./,NR); print $0 }' file
>
> which i indeed something longer... ;-)
>
You could alternatively do:
awk 'BEGIN{
while ((getline var < ARGV[1]) > 0) {
sub(/./,++nr,var)
print var
}
close(ARGV[1])
exit
}' file
if you really need to fill up a file ;-). Just making the point for anyone
else
reading this that while more text can make the script appear to be "more
readable" to non-awk-experienced procedural programmers, it's better to
just get
used to and use the awk idioms than get stuck in a C-like paradigm and
miss all
the benefits of the awk paradigm.
Ed.
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