Download Perl One-Liners: 130 Programs That Get Things Done by Peteris Krumins PDF

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6, except you replace min with max. 9 Replace each field with its absolute value perl -alne 'print "@{[map { abs } @F]}"' This one-liner first auto-splits the line using the -a option. The split fields end up in the @F variable. Next, it calls the absolute value function abs on each field with the help of the map function. Essentially, the map function applies a given function to each element of the list and returns a new list that contains the results of applying the function. For example, if the list @F is (-4, 2, 0), mapping abs over it produces the list (4, 2, 0).

3, except it only numbers and prints lines that match /regex/. It doesn’t print nonmatching lines. 5: record foo bar baz record qux And let’s say you want to number and print only the lines that contain the word record. 7 Number all lines but print line numbers only for lines that match a pattern perl -pe '$_ = "$. 6. Here, the line number is prepended to the line if the line matches a /regex/; otherwise, it’s simply printed without a line number. , $_' This one-liner uses printf to print the line number together with the line contents.

In this loop, each line is read by the diamond operator <> and is placed in the special variable $_, but it’s not printed! You have to print the line yourself—a useful feature if you want to print, modify, or delete lines selectively. In this one-liner, the code is print unless /^$/, so the entire Perl program becomes while (<>) { print unless /^$/ } Unraveling this a bit further, you get this: while (<>) { print $_ unless $_ =~ /^$/ } This one-liner prints all nonblank lines. ) This one-liner also removes all blank lines: perl -lne 'print if length' This one-liner uses the -l command-line argument, which automat­ ically chomps the input line (basically removes the newline at the end) and appends it back at the end of the line when printing.