More Perl One-liners

Some maybe useful perl one-liners here for easy reference.

Some of the tip are from the post:

1
http://www.catonmat.net/blog/perl-one-liners-explained-part-one/

Some are from my own daily usage.

I also found there are posts about useful sed/awk/perl one-liners:

1
2
3
4
http://www.catonmat.net/blog/awk-one-liners-explained-part-one/
http://www.catonmat.net/blog/sed-one-liners-explained-part-one/
http://www.catonmat.net/blog/introduction-to-perl-one-liners/
http://linux.gda.pl/spotkania/sp_13/perl-one-liners.pdf

1.Loop through a file for each line to find the lines matching certain pattern. Then grep those pattern against a file, and print those lines which has a column meets certain criteria.

1
cat file1.txt | perl -nle 'print $1 if /\b(__[0-9a-z]\w+)\b/i;' | sort | uniq | xargs -I , grep , -w fileb.txt | awk '$2==0' | awk '{print $7}' | sort | uniq | xargs -I , grep , -w filec.txt | awk '$8==0' | awk '{print $8," ",$13}' > /tmp/`date +%Y%m%d`.txt

2.Add a blank line before every line.

1
perl -pe 's//\n/' file.txt

3.Remove all blank lines

1
cat file.txt | perl -ne 'print unless /^$/'

4.Remove all consecutive blank lines, leaving just one.

1
cat file.txt | perl -00 -pe ''

5.Compress/expand all blank lines into N consecutive ones.

1
cat 1.txt| perl -00 -pe '$_.="\n"x4'

6.substitute something in a file:

1
perl -pi -e 's/good/bad/g' file.txt

7.same as item-6 but only on lines match something:

1
perl -pi -e 's/good/bad/g if /matched/' file

8.Finding all repeated lines in a file:

1
perl -ne 'print if $a{$_}++' 1.txt

9.Numbering lines in a file:

1
perl -ne 'print "$. $_"' file.txt

or with the ‘-p’ argument:

1
perl -pe '$_ = "$. $_"' file.txt

10.Sum up all the numbers on each line:

1
cat file.txt| perl -MList::Util=sum -alne 'print sum @F'

11.TO see how the above one-liner works, use the Data::Dumper module to get a look at it:

1
cat file.txt| perl -MData::Dumper -alne 'print  Dumper @F'

12.Finding the date 10 days ago:

1
perl -MPOSIX -le '@now = localtime; $now[3] -= 10; print scalar localtime mktime @now'

13.Find the sum of the numbers in the first column:

1
cat file.txt| perl -lane '$sum += $F[0]; END { print $sum }'

14.Getting a list of the names of all users on the system:

1
perl -a -F: -lne 'print $F[4]' /etc/passwd

15.Print the number of non-empty lines in a file:

1
cat file.txt | perl -le 'print scalar(grep{/./}<>)'

16.Print the number of empty lines in a file:

1
cat file.txt| perl -lne '$a++ if /^$/; END {print $a+0}'

or

1
cat file.txt | perl -le 'print scalar(grep{/^$/}<>)'

or

1
cat file.txt | perl -le 'print ~~grep{/^$/}<>'

17.Print the number of lines in a file that match a pattern (emulate grep -c):

1
cat 3.txt| perl -lne '$a++ if /good/; END {print $a+0}'

or

1
cat 3.txt | grep -c "good"

18.Generate and print the alphabet:

1
2
3
4
5
perl -le 'print ("a".."z")'
or
perl -le 'print a..z'
or
perl -le 'print join "", ("a".."z")'

19.Generate a random 8 character password:

1
perl -le 'print map { ("a".."z")[rand 26] } 1..8'

20.Find the numeric values for characters in the string:

1
perl -le 'print join ", ", map { ord } split //, "hello world"'

21.Generate an array with odd numbers from 1 to 100:

1
perl -le '@odd = grep {$_ % 2 == 1} 1..100; print "@odd"'

22.Find the length of the string:

1
perl -le 'print length "hello boy"'

23.Find the number of elements in an array:

1
2
3
4
5
perl -le '@array = ("a".."z"); print ~~@array'
or
perl -le '@array = ("a".."z"); print scalar @array'
or
perl -le '@array = ("a".."z"); print $#array + 1'

24.Base64 encode a string:

1
perl -MMIME::Base64 -e 'print encode_base64("string")'

25.base64 encode the whole file:

1
perl -MMIME::Base64 -0777 -ne 'print encode_base64($_)' file

26.Base64 decode a string:

1
perl -MMIME::Base64 -le 'print decode_base64("c3RyaW5n")'

27.URL-escape a string:

1
perl -MURI::Escape -le 'print uri_escape("1+2")'

28.URL-unescape a string:

1
perl -MURI::Escape -le 'print uri_unescape("1%2B2")'

29.HTML-encode a string:

1
perl -MHTML::Entities -le 'print encode_entities("<br>")'

30.HTML-decode a string:

1
perl -MHTML::Entities -le 'print decode_entities("&lt;br&gt;")'

31.Convert all text to uppercase:

1
cat file | perl -nle 'print uc'

32.Camel case each line:

1
cat file | perl -ple 's/(\w+)/\u$1/g'

33.Strip leading whitespace (spaces, tabs) from the beginning of each line:

1
cat file | perl -ple 's/^[ \t]+//'

34.Strip trailing whitespace (space, tabs) from the end of each line:

1
cat file | perl -ple 's/[ \t]+$//'

35.Strip whitespace from the beginning and end of each line:

1
cat file | perl -ple 's/^[ \t]+|[ \t]+$//g'

36.Substitute (find and replace) “foo” with “bar” on lines that match “baz”:

1
cat file | perl -pe '/baz/ && s/foo/bar/'

37.Print the first line of a file (emulate head -1):

1
cat file | perl -ne 'print; exit'

38.Print the first 10 lines of a file (emulate head -10):

1
perl -ne 'print if $. <= 10'

This one-liner uses the $. special variable. This variable stands for “current line number.”

39.Print the last line of a file:

1
2
3
cat file | perl -ne '$last = $_; END { print $last }'
or
cat file | perl -ne 'print if eof'

40.Print the last 10 lines of a file (emulate tail -10):

1
cat file | perl -ne 'push @a, $_; @a = @a[@a-10..$#a]; END { print @a }'

41.Print only lines that do not match a regular expression:

1
cat file | perl -ne '!/regex/ && print'

42.Print the line before a line that matches a regular expression:

1
cat file | perl -ne '/regex/ && $last && print $last; $last = $_'

43.Print the line after a line that matches a regular expression:

1
cat file | perl -ne 'if ($p) { print; $p = 0 } $p++ if /regex/'

44.Print lines that match regex AAA and regex BBB in any order:

1
cat file | perl -ne '/AAA/ && /BBB/ && print'

45.Print lines that don’t match match regexes AAA and BBB:

1
cat file | perl -ne '!/AAA/ && !/BBB/ && print'

46.Print lines that match regex AAA followed by regex BBB followed by CCC:

1
cat file | perl -ne '/AAA.*BBB.*CCC/ && print'

47.Print lines that are 20 chars or longer:

1
cat file | perl -ne 'print if length >= 80'

48.Print only line 13:

1
cat file | perl -ne '$. == 13 && print && exit'

49.Print all lines except line 13.

1
perl -ne '$. != 13 && print'

50.Print only lines 13, 19 and 67:

1
perl -ne 'print if $. == 13 || $. == 19 || $. == 67'

51.Print all lines between two regexes:

1
cat file | perl -ne 'print if /regex1/../regex2/'

52.Print all lines from line 17 to line 30:

1
cat file | perl -ne 'print if $. >= 17 && $. <= 30'

53.Print the longest line:

1
cat file | perl -ne '$l = $_ if length($_) > length($l); END { print $l }'

54.Print the shortest line:

1
cat file | perl -ne '$s = $_ if $. == 1; $s = $_ if length($_) < length($s); END { print $s }'

55.Print all lines that contain only characters:

1
cat file | perl -ne 'print if /^[[:alpha:]]+$/'

56.Print all lines that repeat:

1
cat file | perl -ne 'print if ++$a{$_} == 2'

57.Print all unique lines:

1
cat file | perl -ne 'print unless $a{$_}++'

58.To remove blank lines:

1
cat file | perl -pi -e 's!^\s+?$!!'