perl one liner

collection of one-liners, a part is adapted from such a list by
Tom Christianson, one of the authors of "Programming Perl".

    # the always present hallo world program, adapted to a Math department
    perl -e 'print "Hello Mr Euler!\n"'

    # rename in each file name the string aaa by bbb
    ls | perl -ne 'chomp; next unless -e; $o = $_; s/aaa/bbb/; next if -e; rename $o, $_';

    # add first and last column in each line of file foo.txt and print it out
    perl -lane 'print $F[0] + $F[-1]' foo.txt

    # print lines 15 to 17 of file foo.txt
    perl -ne 'print if 15 .. 17' foo.txt

    # a second way to print lines 3 to 5 of file foo.txt
    perl -pe 'exit if 3<$. && $.<5' foo.txt

    # change all words "foo"s to "bar"s in every .c file and keep backups
    perl -p -i.bak -e 's/\bfoo\b/bar/g' *.c

    # the same but without backup. Remember the flags: "eat the pie"
    perl -p -i -e 's/foo/bar/g' *.c

    # changes ^M newline characters to newlines
    perl  -p -i -e 's/\012?\015/\n/g'  $1

    # the same but with all files with name filename
    perl -p -i -e  's/foo/bar' `find . -name "filename"`

    # substitution can also be applied to binary files like test.ppm
    perl -p -i -e 's/255/127/g' test.ppm

    # substitute "xyz.math" to "abc.math" in every .html file and keep backups
    perl -p -i.bak -e 's/xyz\.math/abc\.math/g' *.html

    # insert department name after each title and keep backup
    perl -p -i.bak -e 's#<title>#<title>Harvard .: #i' *.html

    # delete first 10 lines in foo.txt and keep backup foo.txt.bak
    perl -i.bak -ne 'print unless 1 .. 10' foo.txt

    # change isolated occurrence of aaa to bbb in each file *.c or *.h
    perl -p -i.bak -e 's{\baaa\b}{bbb}g' *.[ch]

    # reverses lines of file foo.txt and print it
    perl -e 'print reverse <>' foo.txt

    # find palindromes in a dictionary /usr/share/dict/words
    perl -lne 'print if $_ eq reverse' /usr/share/dict/words

    # reverses paragraphs in file foo.txt
    perl -00 -e 'print reverse <>' foo.txt

    # increments all numbers in foo.tx by 1
    perl -pe 's/(\d+)/ 1 + $1 /ge' foo.txt

    # reverses order of characters in each line of foo.txt
    perl -nle 'print scalar reverse $_' foo.txt

    # print lines beween START and END in foo.txt to STDOUT
    perl -ne 'print if /^START$/ .. /^END$/' foo.txt

    # delete lines beween START and END and backup original file
    perl -i.old -ne 'print unless /^START$/ .. /^END$/' foo.txt

    # look for duplicated words in a line
    perl -0777 -ne 'print "$.: doubled $_\n" while /\b(\w+)\b\s+\b\1\b/gi' foo.txt

    # start Perl debugger "stand-alone"
    perl -d -e 42

    # run a Perl program program.pl with warnings
    perl -w program.pl

    # run a Perl program program.pl with debugger
    perl -d program.pl

    # Run perl program program.pl, check syntax, print warnings
    perl -wc program.pl

HOT PERL ONLINERS

   Just enough perl to do most everything! Tom Christianson (spelling?)
   once posted a canonical list of one line perl programs to do many common
   command-line tasks.
   It included:
   # run contents of "my_file" as a program
   perl my_file

   # run debugger "stand-alone"
   perl -d -e 42

   # run program, but with warnings
   perl -w my_file

   # run program under debugger
   perl -d my_file

   # just check syntax, with warnings
   perl -wc my_file

   # useful at end of "find foo -print"
   perl -nle unlink

   # simplest one-liner program
   perl -e 'print "hello world!\n"'

   # add first and penultimate columns
   perl -lane 'print $F[0] + $F[-2]'

   # just lines 15 to 17
   perl -ne 'print if 15 .. 17' *.pod

   # in-place edit of *.c files changing all foo to bar
   perl -p -i.bak -e 's/\bfoo\b/bar/g' *.c

   # command-line that prints the first 50 lines (cheaply)
   perl -pe 'exit if $. > 50' f1 f2 f3 ...

   # delete first 10 lines
   perl -i.old -ne 'print unless 1 .. 10' foo.txt

   # change all the isolated oldvar occurrences to newvar
   perl -i.old -pe 's{\boldvar\b}{newvar}g' *.[chy]

   # command-line that reverses the whole file by lines
   perl -e 'print reverse <>' file1 file2 file3 ....

   # find palindromes
   perl -lne 'print if $_ eq reverse' /usr/dict/words

   # command-line that reverse all the bytes in a file
   perl -0777e 'print scalar reverse <>' f1 f2 f3 ...

   # command-line that reverses the whole file by paragraphs
   perl -00 -e 'print reverse <>' file1 file2 file3 ....

   # increment all numbers found in these files
   perl i.tiny -pe 's/(\d+)/ 1 + $1 /ge' file1 file2 ....

   # command-line that shows each line with its characters backwards
   perl -nle 'print scalar reverse $_' file1 file2 file3 ....

   # delete all but lines beween START and END
   perl -i.old -ne 'print unless /^START$/ .. /^END$/' foo.txt

   # binary edit (careful!)
   perl -i.bak -pe 's/Mozilla/Slopoke/g' /usr/local/bin/netscape

   # look for dup words
   perl -0777 -ne 'print "$.: doubled $_\n" while /\b(\w+)\b\s+\b\1\b/gi'

   # command-line that prints the last 50 lines (expensively)
   perl -e 'lines = <>; print @@lines[ $#lines .. $#lines-50' f1 f2 f3 ...