Using grep on Windows as well

How can you search for all the occurrences of the 'secret' in your xml files?

On Linux and macOS you would probably use grep or egrep. You can also install some kind of grep on MS Windows as well, but if you already have Perl installed then you can use it as well.

In a single file

perl -ne "print if /secret/" main.xml

• -e tells perl to use the parameter as perl code
• -n tells perl to execute that code on every line of the input file and on each iteration put the current line in the default variable called $_.
• print without parameters will print the content of $_.
• /secret/ is regex (the slashes are the delimiters). If no =~ is provided then it works in the content of the default variable called $_.

The above line is the same as the one below:

perl -n -e "print $_ if $_ =~ /secret/" main.xml

Use Deparse to convert the oneliner into full script to make it more readeble.

$ perl -MO=Deparse -ne "print if /secret/" main.xml

LINE: while (defined($_ = readline ARGV)) {
    print $_ if /secret/;
}
-e syntax OK

In multiple files

As Windows does not handle wildcards on the command line, we cannot supply *.xml and expect it to handle all the xml files. We help it with a small BEGIN block. $ARGV holds the name of the current file

perl -ne "BEGIN{ @ARGV = glob '*.xml'} print qq{$ARGV:$_} if /secret/"

• The BEGIN {} construct will be executed once, before we start looping over the lines
• glob '*.xml' is an expression in perl returning the list of all the files in the current folder with xml extension.
• @ARGV is the global variable that holds the command line parameters. Usually it is filled by perl when a script starts. Here we fill it ourselves from inside the perl code.
• The -n flag tells perl to iterate over every line in every file listed in @ARGV. On every iteration the name of the current file is in the $ARGV variable and the current line is in the $_ variable.
• In this example we use the reversed if-statement (do something if some condition).
• /secret/ is a regex checking if the current content of $_ matches the series of characters: secret.

We can use the B::Deparse library to ask perl to show how it understands our code:

$ perl  -MO=Deparse -ne "BEGIN{ @ARGV = glob '*.xml'} print qq{$ARGV:$_} if /secret/"
LINE: while (defined($_ = readline ARGV)) {
    sub BEGIN {
        use File::Glob ();
        @ARGV = glob('*.xml');
    }
    print ':main.xml' if /secret/;
}
-e syntax OK