book

Perl One-Liners

by Peteris Krumins

December 2013

Intermediate to advanced

168 pages

2h 49m

English

No Starch Press

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2.1 Double-space a file2.2 Double-space a file, excluding the blank lines2.3 Triple-space a file2.4 N-space a file2.5 Add a blank line before every line2.6 Remove all blank lines2.7 Remove all consecutive blank lines, leaving only one2.8 Compress/expand all blank lines into N consecutive lines2.9 Double-space between all words2.10 Remove all spacing between words2.11 Change all spacing between words to one space2.12 Insert a space between all characters
3.1 Number all lines in a file3.2 Number only non-empty lines in a file3.3 Number and print only non-empty lines in a file (drop empty lines)3.4 Number all lines but print line numbers only for non-empty lines3.5 Number only lines that match a pattern; print others unmodified3.6 Number and print only lines that match a pattern3.7 Number all lines but print line numbers only for lines that match a pattern3.8 Number all lines in a file using a custom format3.9 Print the total number of lines in a file (emulate wc -l)3.10 Print the number of non-empty lines in a file3.11 Print the number of empty lines in a file3.12 Print the number of lines in a file that match a pattern (emulate grep -c)3.13 Number words across all lines3.14 Number words on each individual line3.15 Replace all words with their numeric positions
4.1 Check if a number is a prime4.2 Print the sum of all fields on each line4.3 Print the sum of all fields on all lines4.4 Shuffle all fields on each line4.5 Find the numerically smallest element (minimum element) on each line4.6 Find the numerically smallest element (minimum element) over all lines4.7 Find the numerically largest element (maximum element) on each line4.8 Find the numerically largest element (maximum element) over all lines4.9 Replace each field with its absolute value4.10 Print the total number of fields on each line4.11 Print the total number of fields on each line, followed by the line4.12 Print the total number of fields on all lines4.13 Print the total number of fields that match a pattern4.14 Print the total number of lines that match a pattern4.15 Print the number π4.16 Print the number e4.17 Print UNIX time (seconds since January 1, 1970, 00:00:00 UTC)4.18 Print Greenwich Mean Time and local computer time4.19 Print yesterday’s date4.20 Print the date 14 months, 9 days, and 7 seconds ago4.21 Calculate the factorial4.22 Calculate the greatest common divisor4.23 Calculate the least common multiple4.24 Generate 10 random numbers between 5 and 15 (excluding 15)4.25 Generate all permutations of a list4.26 Generate the powerset4.27 Convert an IP address to an unsigned integer4.28 Convert an unsigned integer to an IP address
5.1 Generate and print the alphabet5.2 Generate and print all the strings from “a” to “zz”5.3 Create a hex lookup table5.4 Generate a random eight-character password5.5 Create a string of specific length5.6 Create an array from a string5.7 Create a string from the command-line arguments5.8 Find the numeric values for characters in a string5.9 Convert a list of numeric ASCII values into a string5.10 Generate an array with odd numbers from 1 to 1005.11 Generate an array with even numbers from 1 to 1005.12 Find the length of a string5.13 Find the number of elements in an array
6.1 ROT13 a string6.2 Base64-encode a string6.3 Base64-decode a string6.4 URL-escape a string6.5 URL-unescape a string6.6 HTML-encode a string6.7 HTML-decode a string6.8 Convert all text to uppercase6.9 Convert all text to lowercase6.10 Uppercase only the first letter of each line6.11 Invert the letter case6.12 Title-case each line6.13 Strip leading whitespace (spaces, tabs) from the beginning of each line6.14 Strip trailing whitespace (spaces, tabs) from the end of each line6.15 Strip whitespace (spaces, tabs) from the beginning and end of each line6.16 Convert UNIX newlines to DOS/Windows newlines6.17 Convert DOS/Windows newlines to UNIX newlines6.18 Convert UNIX newlines to Mac newlines6.19 Substitute (find and replace) “foo” with “bar” on each line6.20 Substitute (find and replace) “foo” with “bar” on lines that match “baz”6.21 Print paragraphs in reverse order6.22 Print all lines in reverse order6.23 Print columns in reverse order
7.1 Print the first line of a file (emulate head -1)7.2 Print the first 10 lines of a file (emulate head -10)7.3 Print the last line of a file (emulate tail -1)7.4 Print the last 10 lines of a file (emulate tail -10)7.5 Print only lines that match a regular expression7.6 Print only lines that do not match a regular expression7.7 Print every line preceding a line that matches a regular expression7.8 Print every line following a line that matches a regular expression7.9 Print lines that match regular expressions AAA and BBB in any order7.10 Print lines that don’t match regular expressions AAA and BBB7.11 Print lines that match regular expression AAA followed by BBB followed by CCC7.12 Print lines that are at least 80 characters long7.13 Print lines that are fewer than 80 characters long7.14 Print only line 137.15 Print all lines except line 277.16 Print only lines 13, 19, and 677.17 Print all lines from 17 to 307.18 Print all lines between two regular expressions (including the lines that match)7.19 Print the longest line7.20 Print the shortest line7.21 Print all lines containing digits7.22 Print all lines containing only digits7.23 Print all lines containing only alphabetic characters7.24 Print every second line7.25 Print every second line, beginning with the second line7.26 Print all repeated lines only once7.27 Print all unique lines

8.1 Match something that looks like an IP address8.2 Test whether a number is in the range 0 to 2558.3 Match an IP address8.4 Check whether a string looks like an email address8.5 Check whether a string is a number8.6 Check whether a word appears in a string twice8.7 Increase all integers in a string by one8.8 Extract the HTTP User-Agent string from HTTP headers8.9 Match printable ASCII characters8.10 Extract text between two HTML tags8.11 Replace all <b> tags with <strong>8.12 Extract all matches from a regular expression
A.1 Variable $_Using $_ with the -n argumentUsing $_ with the -p argumentUsing $_ explicitlyA.2 Variable $.A.3 Variable $/A.4 Variable $\A.5 Variables $1, $2, $3, and so onA.6 Variable $,A.7 Variable $”A.8 Variable @FA.9 Variable @ARGVA.10 Variable %ENV
B.1 Perl on WindowsB.2 Bash on WindowsB.3 Perl One-Liners in Windows BashB.4 Perl One-Liners in the Windows Command PromptConverting One-Liners in the Windows Command PromptSymbol ChallengesWindows File PathsB.5 Perl One-Liners in PowerShellConverting One-Liners in PowerShellOne-Liners in PowerShell 3.0+
C.1 Spacing Double-space a fileDouble-space a file, excluding the blank linesTriple-space a fileN-space a fileAdd a blank line before every lineRemove all blank linesRemove all consecutive blank lines, leaving only oneCompress/expand all blank lines into N consecutive linesDouble-space between all wordsRemove all spacing between wordsChange all spacing between words to one spaceInsert a space between all charactersC.2 Numbering Number all lines in a fileNumber only non-empty lines in a fileNumber and print only non-empty lines in a file (drop empty lines)Number all lines but print line numbers only for non-empty linesNumber only lines that match a pattern; print others unmodifiedNumber and print only lines that match a patternNumber all lines but print line numbers only for lines that match a patternNumber all lines in a file using a custom formatPrint the total number of lines in a file (emulate wc -l)Print the number of non-empty lines in a filePrint the number of empty lines in a filePrint the number of lines in a file that match a pattern (emulate grep -c)Number words across all linesNumber words on each individual lineReplace all words with their numeric positionsC.3 Calculations Check if a number is a primePrint the sum of all fields on each linePrint the sum of all fields on all linesShuffle all fields on each lineFind the numerically smallest element (minimum element) on each lineFind the numerically smallest element (minimum element) over all linesFind the numerically largest element (maximum element) on each lineFind the numerically largest element (maximum element) over all linesReplace each field with its absolute valuePrint the total number of fields on each linePrint the total number of fields on each line, followed by the linePrint the total number of fields on all linesPrint the total number of fields that match a patternPrint the total number of lines that match a patternPrint the number πPrint the number ePrint UNIX time (seconds since January 1, 1970, 00:00:00 UTC)Print Greenwich Mean Time and local computer timePrint yesterday’s datePrint the date 14 months, 9 days, and 7 seconds agoCalculate the factorialCalculate the greatest common divisorCalculate the least common multipleGenerate 10 random numbers between 5 and 15 (excluding 15)Generate all permutations of a listGenerate the powersetConvert an IP address to an unsigned integerConvert an unsigned integer to an IP addressC.4 Working with Arrays and Strings Generate and print the alphabetGenerate and print all the strings from “a” to “zz”Create a hex lookup tableGenerate a random eight-character passwordCreate a string of specific lengthCreate an array from a stringCreate a string from the command-line argumentsFind the numeric values for characters in a stringConvert a list of numeric ASCII values into a stringGenerate an array with odd numbers from 1 to 100Generate an array with even numbers from 1 to 100Find the length of a stringFind the number of elements in an arrayC.5 Text Conversion and Substitution ROT13 a stringBase64-encode a stringBase64-decode a stringURL-escape a stringURL-unescape a stringHTML-encode a stringHTML-decode a stringConvert all text to uppercaseConvert all text to lowercaseUppercase only the first letter of each lineInvert the letter caseTitle-case each lineStrip leading whitespace (spaces, tabs) from the beginning of each lineStrip trailing whitespace (spaces, tabs) from the end of each lineStrip whitespace (spaces, tabs) from the beginning and end of each lineConvert UNIX newlines to DOS/Windows newlinesConvert DOS/Windows newlines to UNIX newlinesConvert UNIX newlines to Mac newlinesSubstitute (find and replace) “foo” with “bar” on each lineSubstitute (find and replace) “foo” with “bar” on lines that match “baz”Print paragraphs in reverse orderPrint all lines in reverse orderPrint columns in reverse orderC.6 Selectively Printing and Deleting Lines Print the first line of a file (emulate head -1)Print the first 10 lines of a file (emulate head -10)Print the last line of a file (emulate tail -1)Print the last 10 lines of a file (emulate tail -10)Print only lines that match a regular expressionPrint only lines that do not match a regular expressionPrint every line preceding a line that matches a regular expressionPrint every line following a line that matches a regular expressionPrint lines that match regular expressions AAA and BBB in any orderPrint lines that don’t match regular expressions AAA and BBBPrint lines that match regular expression AAA followed by BBB followed by CCCPrint lines that are at least 80 characters longPrint lines that are fewer than 80 characters longPrint only line 13Print all lines except line 27Print only lines 13, 19, and 67Print all lines from 17 to 30Print all lines between two regular expressions (including the lines that match)Print the longest linePrint the shortest linePrint all lines containing digitsPrint all lines containing only digitsPrint all lines containing only alphabetic charactersPrint every second linePrint every second line, beginning with the second linePrint all repeated lines only oncePrint all unique linesC.7 Useful Regular Expressions Match something that looks like an IP addressTest whether a number is in the range 0 to 255Match an IP addressCheck whether a string looks like an email addressCheck whether a string is a numberCheck whether a word appears in a string twiceIncrease all integers in a string by oneExtract the HTTP User-Agent string from HTTP headersMatch printable ASCII charactersExtract text between two HTML tagsReplace all <b> tags with <strong>Extract all matches from a regular expression

Content preview from Perl One-Liners

Chapter 1. Introduction to Perl One-Liners

Perl one-liners are small and awesome Perl programs that fit in a single line of code. They do one thing really well—like changing line spacing, numbering lines, performing calculations, converting and substituting text, deleting and printing specific lines, parsing logs, editing files in-place, calculating statistics, carrying out system administration tasks, or updating a bunch of files at once. Perl one-liners will make you a shell warrior: what took you minutes (or even hours) to solve will now take you only seconds!

In this introductory chapter, I’ll show you what one-liners look like and give you a taste of what’s in the rest of the book. This book requires some Perl knowledge, but most of the one-liners ...