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!
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