[CentOS] Assitance with perl

Thu Feb 3 01:54:38 UTC 2022
H <agents at meddatainc.com>

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!