perl:tldr:f3210

This command consists of two parts joined together by the pipe "|" symbol.

Part 1: cat ${filename}

• The "cat" command is used to output the content of a file.
• ${filename} represents a placeholder for the actual filename or path of the file you want to display the content of.
• This part will output the content of the specified file.

Part 2: perl -n -l -e 'print $1 if /${before}(${regular_expression})${after}/'

• The "perl" command is used to execute Perl code.
• "-n" option is used to loop over the input file line by line.
• "-l" option is used to automatically add newlines to print statements.
• "-e" option indicates that the following argument is the Perl code to be executed.
• 'print $1 if /${before}(${regular_expression})${after}/' is the Perl code to be executed.
  • "${before}", "${regular_expression}", and "${after}" represent placeholder variables that should be replaced with actual values.
  • "/${before}(${regular_expression})${after}/" is a regular expression enclosed in forward slashes.
  • $1 is a Perl variable that represents the first captured group (content within parentheses) in the regular expression.
• This part will search for lines in the input (content of the file) that match the specified regular expression pattern, and if found, it will print the first captured group ($1) in those lines.

Overall, this command displays the content of a file and searches for lines that match a specific regular expression pattern, printing the first captured group from those lines.