- perl provides many command line switches to control how a Perl script is executed or the input/output behavior. Some key switches include -n, -p, -l, -e, -M, -I, -V, and -E. - Special variables like $. and eof can be used to access the current line number or detect the end of input files when iterating over lines. - Modules can be loaded at startup using -M to enhance functionality, and %INC shows where modules were loaded from. - Various quoting mechanisms like qq can be used to specify strings without interpolation.

1. Perl One Liners for the Shell

2. Dave Oswald
● Conferences Committee
Chairman
● Salt Lake Perl Mongers
Organizer
● Software Engineer
● Platform & Infrastructure
Engineering Manager

6. perl [switches] [--] [programfile]
[arguments]

7. Switches
-0[octal] specify record separator (0, if no argument)
-a autosplit mode with -n or -p (splits $_ into @F)
-C[number/list] enables the listed Unicode features
-c check syntax only (runs BEGIN and CHECK blocks)
-d[:debugger] run program under debugger
-D[number/list] set debugging flags (argument is a bit mask or alphabets)
-e program one line of program (several -e's allowed, omit programfile)
-E program like -e, but enables all optional features
-f don't do $sitelib/sitecustomize.pl at startup
-F/pattern/ split() pattern for -a switch (//'s are optional)
-i[extension] edit <> files in place (makes backup if extension supplied)
-Idirectory specify @INC/#include directory (several -I's allowed)
-l[octal] enable line ending processing, specifies line terminator
-[mM][-]module execute "use/no module..." before executing program
-n assume "while (<>) { ... }" loop around program
-p assume loop like -n but print line also, like sed
-s enable rudimentary parsing for switches after programfile
-S look for programfile using PATH environment variable
-t enable tainting warnings
-T enable tainting checks
-u dump core after parsing program
-U allow unsafe operations
-v print version, patchlevel and license
-V[:variable] print configuration summary (or a single Config.pm variable)
-w enable many useful warnings
-W enable all warnings
-x[directory] ignore text before #!perl line (optionally cd to directory)
-X disable all warnings

10. perldoc perlrun

11. Introducing the tools

12. perl -e ''

13. -e

14. perl -e 'print "Hello World!n"'
Hello World!

15. #!/usr/bin/env perl
print 'Hello World!n';
Hello World!

16. echo 'Hello World'

17. while (defined(local $_ = <>)) {
...
print;
}
$ perl myscript file1.txt file2.txt

18. Internally <> reads from each file in @ARGV, falling
back to STDIN.

19. A concept in Perl is only valid if it can be
expressed as a one-liner.
-- Documentation for Inline::C

20. perl -pe '...'

21. while (defined(local $_ = <>)) {
...
print;
}
$ perl myscript file1.txt file2.txt

22. while (defined(local $_ = <>)) {
chomp
...
$_ .= "n";
print;
}
$ perl myscript file1.txt file2.txt

23. perl -lpe '...'

24. Reverse the characters in every word in a
dictionary

25. perl -ple '$_ = reverse'
~/scripts/2of12inf.txt

26. Count by fives

27. seq 1 10 | perl -lpe '$_ *= 5'

28. -l
chomps input, adds newline to output.

29. -l
chomps input, adds newline to output.
$/ = $ = "n"

30. -p
Creates a loop that iterates over lines of input,
carries out any actions in the code block, and
prints each line.

31. $.

32. perl -pe '$_ = "$. " . $_'
2of12inf.txt

33. $.
Special variable contains the line number of the
most recently read line of input.
Lines start at 1.

34. Sometimes printing every line of input is not
wanted.

35. -n

36. perl -ne 'print "$.: $_" if m/^th/'
2of12inf.txt

37. Let’s get a count at the end.

38. This means we need something to happen only
one time, after the loop is done.

39. perl -ne 'if (m/^th/) {$c++; print} END{print
"$cn"}'

40. grep '^th' 2of12inf.txt |wc -l

41. -n iterates over lines of a file without printing.
You can print explicitly.

42. -n is useful as a filter similar to GNU grep.

43. END{ ... }
Can be used to defer an action to after the
iterating is done.

44. Input can come from STDIN rather than a file.
This allows pipes to work.

45. seq 1 10 |perl -ne '$_*=5; print "$_n" if $_ % 3
== 0'

46. perl -l0pe '...' filename

47. -l0
Specify an octal ASCII value as input/output
record separator.

48. -0
Set output record separator to octal value

49. -0oct and -loct
Useful for working with null-terminated lines or
input.

50. -a

51. df |perl -ane 'next if $. == 1; print "$F[-1]
$F[-2]n"'

52. -a
Auto-split each line on whitespace into @F

53. Let’s split on comma and change to colon

54. -F/pattern/

55. perl -F/,/ -ne '$"=":"; print "@F";'
csv

56. -F/pattern/
Specifies an alternate split pattern.

57. $" = "..."
Specifies an alternate “join” delimiter when an
array is interpolated into a string.

58. perl -pe 'tr/,/:/' csv

59. -i

60. perl -i.bak -pe 'tr/,/:/' csv

61. -i
In-place edit a file.
Optionally create a backup of original.

62. perl -i.bak -pe 'tr/:/,/' csv

63. Fixed.

65. Handling multiple files distinctly

66. eof

67. perl -ne 'print; print "EOFn" if eof'
2of12inf.txt

68. Use eof to detect end of input files.

69. -M

70. Load a module at startup

71. seq 1 10 |perl -MList::Util=shuffle
-ne 'push @S, $_; END{print for
shuffle @S}'

72. seq 1 10 |perl -MList::Util=shuffle
-ne
'push @S, $_; END{print for shuffle
@S}'

73. -M
Loads a module at startup.
Optionally specify an import list.

74. May invoke -M more than once.

75. perl -Mstrict -Mwarnings -e '$foo=10'
(Strict violation)

76. What modules are loaded when I load
Data::Dumper?

77. perl -MData::Dumper -e 'print "$_n" for keys
%INC'

78. Where is Perl finding Data::Dumper?

79. perl -MData::Dumper -e 'print qq/
$INC{"Data/Dumper.pm"}n/'

80. qq/.../
Same as "..."
Used to specify an alternate quoting mechanism

81. q/.../ '...'
qq/.../ '...'
qr/.../ m/.../
qx/.../ `...`

82. q{...} '...'
qq{...} '...'
qr{...} m/.../
qx{...} `...`

83. %INC
Hash containing list of modules loaded, and their
file paths.

84. -E

85. perl -MData::Dumper -E 'say
$INC{"Data/Dumper.pm"}'

86. -E
Allow use of say keyword.
say is like print, but auto-appends newline.

87. -E
Also enables all feature keywords for the Perl
version in use.

88. -I

89. perl -I/path/to/lib -MGreet -E 'say
greet()'

90. perl -I./lib -E 'say for @INC';

91. -I
Specify the first path to search for a module.
Multiple -I switches are fine.

92. -V

93. perl -V

94. perl -V:u64type

95. perl -MConfig -E 'say
$Config{u64type}'

96. Find all mentions of a feature in Perl POD
"*delta.pod" articles for current version of Perl.

97. How do I know when feature X was
added to Perl?

98. How do I know when feature X was
added to Perl?
grep -ri 'signatures' $(find $(perl -E 'say for @INC')
-name '*delta.pod')

99. Perl's documentation

100. Perl's documentation
● perlrun
– Explanation of all command-line switches.
● perlvar
– Explanation of Perl's "special variables"
● perlsyn
– Description of syntax

101. Perl is part of Linux's rich set of tools.

102. daoswald@gmail.com
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