How to append after Regex Search in Perl script - regex

Question

I'm trying to convert a MySQL dump into SQLite database, for database migration. I need to edit the date to append time, so for example 2018-09-19 should be converted to 2018-09-19 00:00:00.00. The reason for this format has to do with how our application works. This is the solution I came up with but it doesn't work.
#!/usr/bin/perl
while (<>){
<Other Stuff>
....
s/([12]\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01]))\[/$1[00:00:00.00]][/
print;
}
For testing I created a test.txt file with just for testing
2019-03-06
And in command line or terminal I used the following command to test if the append works.
perl -pe 's/([12]\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01]))\[/$1[00:00:00.00]][/' < test.txt > testout.txt
This gives a clear error of:
syntax error at -e line 1, near "00:" Execution of -e aborted due to compilation errors.
Using this #dada's solution that looks like this gives no error but also doesn't append the 00:00:00.00 at the end of the line
The Expected output should be
2019-03-06 00:00:00.00

Answer 1

Your problem statement says you want to turn:
2018-09-19
into:
2018-09-19 00:00:00.00
However, your code is:
s/([12]\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01]))\[/$1[00:00:00.00]][/
Using /x we can write it a bit more legibly as:
s/
(
[12]\d{3} # year
- # hyphen
( 0[1-9] | 1[0-2] ) # month (saved as $2)
- # hyphen
( 0[1-9] | [12]\d | 3[01] ) # day (saved as $3)
) # save this as $1
\[ # square bracket
/$1[00:00:00.00]][/x
From this, it is clear that 2018-09-19 does not match because it does not end with a square bracket.
The replacement value is:
$1[00:00:00.00]][
This (tries to) say:
lookup index 00:00:00.00 in array #1 and substitute value
append ][
However this is not valid perl and not what you wanted anyway.
What is happening is that instead of $x + [y] (scalar followed by string value), perl is seeing $x[y] (value from array). To prevent this, either use braces ( ${x}[y] ) or escape the bracket ( $x\[y] ). This results in:
${1}[00:00:00.00]][
which is still not what the problem said was needed as the zeros are wrapped in brackets.
To get what you say you want, remove the \[ from the end of the search part and remove the unnecessary brackets from the replacement part:
s/
(
[12]\d{3}
- ( 0[1-9] | 1[0-2] )
- ( 0[1-9] | [12]\d | 3[01] )
)
# no bracket here
/$1 00:00:00.00/x; # no brackets here
Note that your code as given has another bug which is that the final print needs to be separated from the s/// by a semi-colon.