CentOS - Feb 2022 - Assitance with perl

On 01/30/2022 11:00 PM, Orion Poplawski wrote:
> On 1/30/22 18:12, H wrote:
>> I am writing a long bash script under CentOS 7 where perl is used for
manipulating some external files. So far I am using perl one-liners to do so but
ran into a problem when I need to append text to an external file.
>>
>> Here is a simplified example in the bash script where txt is a bash
variable which I built containing a longish text with multiple newlines:
>>
>> txt="a b$'\n'cd ef$'\n'g h$'\n'ij kl"
>>
>> A simplified perl one-liner to append the text in the variable above to
some file in the bash script would be:
>>
>> perl -pe 'eof && do{print $_'"${txt}"';
exit}' someexternalfile.txt
>>
>> This works when fine when $txt does /not/ contain any spaces but falls
apart when it does.
>>
>> I would like to keep the above structure, ie using bash variables to
build text strings and one-liners to do the text manipulation. Hopefully there
is a "simple" solution to do this, I have tried many variations and
failed miserably... Note that I also want to use a similar pattern to do
substitutions in external files, I would thus like to use the same code pattern.
>
> I don't understand why:
>
> echo -e $txt >> someexternalfile.txt
>
> doesn't do what you want, or if perl is absolutely what you need:
>
> perl -e "print \"${txt}\";" >>
someexternalfile.txt
>
> I have no idea if you are trying to output literal $'s or 's or
not.
>
Thank you, it works! I had forgotten to escape the quotes around my bash
variable...

On 01/31/2022 09:59 PM, H wrote:
> On 01/30/2022 11:00 PM, Orion Poplawski wrote:
>> On 1/30/22 18:12, H wrote:
>>> I am writing a long bash script under CentOS 7 where perl is used
for manipulating some external files. So far I am using perl one-liners to do so
but ran into a problem when I need to append text to an external file.
>>>
>>> Here is a simplified example in the bash script where txt is a bash
variable which I built containing a longish text with multiple newlines:
>>>
>>> txt="a b$'\n'cd ef$'\n'g h$'\n'ij
kl"
>>>
>>> A simplified perl one-liner to append the text in the variable
above to some file in the bash script would be:
>>>
>>> perl -pe 'eof && do{print
$_'"${txt}"'; exit}' someexternalfile.txt
>>>
>>> This works when fine when $txt does /not/ contain any spaces but
falls apart when it does.
>>>
>>> I would like to keep the above structure, ie using bash variables
to build text strings and one-liners to do the text manipulation. Hopefully
there is a "simple" solution to do this, I have tried many variations
and failed miserably... Note that I also want to use a similar pattern to do
substitutions in external files, I would thus like to use the same code pattern.
>> I don't understand why:
>>
>> echo -e $txt >> someexternalfile.txt
>>
>> doesn't do what you want, or if perl is absolutely what you need:
>>
>> perl -e "print \"${txt}\";" >>
someexternalfile.txt
>>
>> I have no idea if you are trying to output literal $'s or 's or
not.
>>
> Thank you, it works! I had forgotten to escape the quotes around my bash
variable...
>
I am still having a problem. The following (where $txt is an arbitrary string)
works:

perl -e 'print '"\"${txt}\""';'

The following does not work (I want to append the content of the $txt to the end
of an existing file in-place):

perl -i -pe 'eof && do{print
$_''\"aaa\"''; exit}' somefile.txt

but this does:

perl -i -pe "eof && do{print
$_""\"${txt}\""'; exit}' somefile.txt

as does:

perl -i -pe "eof && do{print
$_""\"${txt}\"""; exit}" somefile.txt

The difference is that the last two perl command strings use " rather than
'.

My questions are:

- Why would not using single-quotes for parts of the perl command string work?

- Is there any reason I should fight this or should I just go with double-quotes
for all parts of the perl command string? Any downside? Remember, these are all
in bash scripts and I am looking for a "pattern" to use for other,
more complicated text substitutions, hence the use of perl.

Thank you!