Inserting Variable Through Perl

Abhay_Anand has asked for the wisdom of the Perl Monks concerning the following question:

Hi I am trying to insert a variable in 2nd line of a file. But it never takes variable value rather keeps taking it as text.

  root@vm-test-001:~/mongosearch# part=( "${arr[@]:i:batchsize}" )
  root@vm-test-001:~/mongosearch# echo $part
  "C:00000092666270:53882159774"
  
  root@vm-test-001:~/mongosearch# perl -ni -e 'print; print "permissib
+leCars = [ \${part[*]} ]\n" if $. == 2' query/containerId_count.js
[download]

This keeps inserting $part as text like permissibleCars = [ ${part*} ] and not as variable like permissibleCars = "C:00000092666270:53882159774" How can this get fixed ?

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Re: Inserting Variable Through Perl by hippo (Archbishop) on Aug 17, 2017 at 07:55 UTC
This is a problem with the shell, not with perl. If you use single quotes in the shell it won't interpolate. eg. `$ part="C:00000092666270:53882159774" $ echo $part C:00000092666270:53882159774 $ echo '$part' $part` [download] Use double-quotes to interpolate or (easier) just unquote the variable when you want to use it. Better still, put it in the environment so perl can access it through `%ENV`.	[reply] [d/l] [select]
Re: Inserting Variable Through Perl by haukex (Archbishop) on Aug 17, 2017 at 07:59 UTC
You can use %ENV to access environment variables, or as a trick you can use the `-s` switch: `$ cat test.txt one two three $ part="C:00000092666270:53882159774" $ echo $part C:00000092666270:53882159774 $ perl -pse 'print qq{foo = [ "$bar" ]\n} if $. == 3' -- -bar="$part" +test.txt one two foo = [ "C:00000092666270:53882159774" ] three $ export part $ perl -pe 'print qq{foo = [ "$ENV{part}" ]\n} if $. == 3' test.txt one two foo = [ "C:00000092666270:53882159774" ] three` [download] I removed the `-i` for demonstration purposes, you can just add it back in, also I used `-p` instead of `-n` to save a bit of typing, but neither of those changes are necessary for the ideas I'm showing to work. Although personally, I usually prefer to just write the whole thing in Perl instead of intermixing Perl and shell scripting.	[reply] [d/l] [select]