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perl:tldr:d4051
The given command performs a specific task using the cat
command, perl
interpreter, and regular expressions.
Here's a breakdown of the command:
-
cat ${filename}
: Thecat
command is used to concatenate and display the contents of the file specified by${filename}
variable. The${filename}
represents a placeholder for an actual filename or path that should be provided when executing the command. -
|
: The pipe symbol (|
) is used to redirect the output of the previous command (cat
) as input for the next command (perl
) in the command pipeline. -
perl -n -l -e 'print if /${regular_expression}/'
: This part executes theperl
interpreter with a specific command-line options (-n -l -e
). The options are explained below:-n
option: Specifies thatperl
should run a loop around the code provided by the following-e
option.-l
option: Enables automatic line-ending processing. It removes the newline character from the input and appends it while printing.-e
option: Allows to specify a Perl program on the command line.
The Perl program provided in single quotes (
'...'
) is:print if /${regular_expression}/
. Here's what it does:print if /${regular_expression}/
: It checks if the current line (provided by-n
option) matches the regular expression${regular_expression}
. If it does, the line is printed to the output. Otherwise, it is skipped.
So, in summary, the command reads the contents of the ${filename}
file, one line at a time. It then checks each line against the ${regular_expression}
and prints only the lines that match the regular expression.