How can I add variables into my Perl one-liner?

Question

I've got the following one-liner with Perl:

perl -MLingua::EN::Sentence=get_sentences -ne 'print "$_\n" for grep { /replace_me/i } @{get_sentences($_)}' "${filePath}"

How can I restructure this so that I'm able to replace the "replace_me" section with any string of text (aka, a variable) that I can pass into the script as an argument?

I understand that you cannot add variables within single quotes, but I'm not sure how to restructure this at the moment with double quotes. Any help would be appreciated.

Answer 1

A "one-liner" is a program that can take input like any other -- what is passed to the program at invocation is in @ARGV array.

Then there are two particular issues to take into account

• With -n the code under '' is the body of a loop (over lines from the files that are processed or from STDIN) so you want to extract your input (arguments) in a BEGIN block, before the runtime and so before the loop starts

• Arguments that are passed to the script must be removed from @ARGV so that what remains are only filename(s), to be read line by line (under -n, or -p)

Then there are three ways to bring arguments into the program.

Fetch the arguments from @ARGV by hand

perl -wnE'BEGIN { $input = shift };  ... '  "input string" filename(s)

where ... stand for your code, just as it was, but which now can use $input.

Another way is with -s switch which enables a rudimentary mechanism for arguments

perl -s -wnE'...code using $input...' -- -input="input string"  filename(s)

where the name given after - (I used input above) is the name of the variable in which input gets stored. The -- are there to mark the beginning of the arguments. All arguments passed to the script must be given before the filename(s).

Finally, instead of passing arguments directly we can set a shell variable which the script will then see. In bash shell we can do it in the same command-line, right before the command itself

input="input string"  perl -wnE'...$ENV{input}...' filenames

Or, set it up beforehand and export it

export input="input string"
perl -wnE'... $ENV{input} ...'

See this post for details on all three ways.

Once this input is used in a regex escape it using quotemeta, /...\Q$input\E.../i, unless it is meant to be a ready regex pattern. Please see the linked documentation.

Answer 2

There are three primary ways of passing information to Perl without using STDIN or external storage.

• Arguments

  perl -ne'BEGIN { $text=shift(@ARGV) } print if /\Q$text/i' -- "$text"
  

• Command-line options

  In a full program, you'd use Getopt::Long, but perl -s will do fine here.

  perl -sne'print if /\Q$text/i' -- -text="$text" --
  

• Environment variables

  TEXT="$text" perl -ne'print if /\Q$ENV{TEXT}/i' --
  

---

In your case, you could use the following:

perl -ne'
   use Lingua::EN::Sentence qw( get_sentences );
   CORE::say for grep { /\Q$text/i } @{ get_sentences($_) };
' -- -text="$text" -- "$filePath"

I used /Q$text/i instead of /$text/i because I assumed the input is text to find rather than a regex pattern. \Q..\E converts text into a pattern that will match that text. (The \E is optional at the end of the literal.)

Answer 3

Provided that you have REPLACEMENT environment variable defined:

export REPLACEMENT=replace_me

You should be able to do either:

perl -MLingua::EN::Sentence=get_sentences -ne 'print "$_\n" for grep { /'$REPLACEMENT'/i } @{get_sentences($_)}' "${filePath}"

or:

perl -MLingua::EN::Sentence=get_sentences -ne 'print "$_\n" for grep { /$ENV{REPLACEMENT}/i } @{get_sentences($_)}' "${filePath}"

It probably also would be wise to quote the string used in the regexp with \Q and \E, e.g. grep { /\Q$ENV{REPLACEMENT}\E/i }.