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AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields Variables Numbers Strings Arrays Sorting Functions One-Liners AWK – Introduction Kurt Schmidt Dept. of Computer Science, Drexel University October 19, 2017

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Page 1: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK – Introduction

Kurt Schmidt

Dept. of Computer Science, Drexel University

October 19, 2017

Page 2: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Intro

Page 3: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK

Works well with record-type dataReads input file(s) a line (record) at a timeParses each record into fieldsPerforms actions on each record that matches a giventestRich math and string libraries

Page 4: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Common Uses

Data validationDoes every record have the same number of fields?Do values make sense (negative values, correct type,etc.)

CalculationsFiltering out/reformatting certain fieldsSearches

Who got a zero on lab 3?Who got the highest grade?

Many others

Page 5: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK versions

Note, on your system awk might be linked to one of these:

awk Original implementation of AWK

nawk New AWK. Sorta AWK 2.0

gawk Gnu’s implementation of AWK

mawk A very fast implementation of AWK

There are others.

Page 6: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Invocation

Can write short programs right on the commmand line(very handy)

print the 3rd field of every line:

$ awk ’{print $3}’ input.txt

To execute an awk script:

$ awk -f script.awk input.txt

Or, use this sha-bang, make the script executable:1

#!/usr/bin/awk -f

1Not so portable. Tough to get env to work here.

Page 7: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK Programs

Page 8: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Processing Input

Input file(s) are read, a record (line) at a timeFiles named on the command line are processed, inorderIf no arguments are given, stdin is read

Each line is checked against each pattern (test), inorder of appearanceFor each pattern that matches, corresponding actionsare performed on that record

Page 9: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Form of an AWK Program

An AWK program is a sequence of function definitions andone or more rules :

pattern {actions}

pattern – Text. Numeric or string relational operator, orregular expression match

If empty, actions are applied to every record

action – Statement or sequence of statementsIf empty, default action is to print the entire line

Page 10: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Patterns

Any numeric or string relational operatorNormal logical operators, too ( && ‖ !)AWK also has regular expression matches

REs are delimited by / /

$3>0 # print all lines where field 3 is greater than 0$1=="Ben" # Find Ben’s record/[Zz]+czc/ # print all lines that contain a match for RE$5~/[Ww]aldo/ # print record if Waldo is hiding in field 5

Page 11: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Patterns

There are two special patterns:BEGIN – True before first record is parsedEND – True after last record is parsed

Empty test applies to every record

BEGIN { print "This happens once, before records are read" }{ sum += $1 } # Sum all values in column 1END {

printf( "Read %d records. Sum of column 1 is %f\n", NR, sum )}

BEGIN { FS="," } # Change field separator, parse CSVs$4==100 { cnt += 1 }END {

printf( "%d students got 100% on midterm.\n", cnt )}

Page 12: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Actions

One or more AWK statementsDefault action is to print entire record ($0)

NR==1 { # Assume first record is column headersfor( i=1; i<=NF; ++i )

print i, $i # show headers}

# print name, studID for section 2NR>1 && $2=="002" { print $4,$5,$7 }

BEGIN { FS="," } # Change field separator, parse CSVs$4==100 { cnt += 1 }END {

printf( "%d students got 100% on midterm.\n", cnt )}

Page 13: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK Language

Page 14: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK is a C-like Scripting Language

Syntax is rather C-likeSame keywords, branches, loops, operators

Only 2 types: numbers (floats) and stringsVariables are dynamically typed – no declarationsLine comments begin with #Statements are separated by newline, or semicolon (;)Arrays are associative

Page 15: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Fields

Fields are split over FSBy default, split over arbitrary whitespace

Fields are identified by $1 $2 $3 ... $NF

NF holds the number of fields in the current record$0 is the current record

{print $0} # print entire line{print $1, $3} # print 1st & 3rd field of each record

Page 16: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Variables

Not declared – dynamic typingSame rules for naming identifiers as C, Java, etc.$n refers to the nth field, where n evaluates to someinteger

{for( i=1; i<=NF; ++i )

print i, $i # enumerate, print each field in the record}

Variables are either all global, or local to the functionthey’re defined in

Page 17: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Some Built-in Variables

NF Number of fields in current record

NR The number of records read (so far)1

FNR The number of records read in this file (so, theline #)

FS Input field separator

OFS Output field separator

RS Input record separator

ORS Output record separator

1Continual count, across files

Page 18: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Numbers

Numbers, and arithmetic operators, are all float typeModulus (%) is an fmod operation

b ∗ int(a/b) + (a%b) == a always holds

There is an int() castAWK uses ˆ and **1for exponentiationAWK uses functions for bit-wise operations:and compl lshift or rshift xor

Same increment, decrement, and op-assn operators

1Don’t use the latter one

Page 19: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

String Concatenation

Accomplished simply by juxtapositionMight be helpful to put parentheses around numbers tobe concatenated on to a string

$ awk ’BEGIN {print -12 " " -24}’-12-24$ awk ’BEGIN {print -12 " " (-24) }’-12 -24

Also a good idea to put parentheses aroundconcatenated expressions

a = "some"b = "file"print "And I’m spinning..." > a b

vs.print "And I’m spinning..." > (a b)

Page 20: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

String Library Functions

length tolowertoupper

Typical string functions

index match Finding substrings1

substr Pulling out substrings

sub gsub gensub Search and replace

split patsplit Return an array of strings

sprintf Returns a formatted string

strtonum Pulls numeric value from string

1Strings can not be indexed directly

Page 21: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Arrays

All arrays are associativeKeys can be numbers or stringsVectors can be sparse

a1.awk

BEGIN {a[1]="kurt"a[2]=13a[3]="Ski"for( k in a )

print k, a[k]}

output:

1 kurt2 133 Ski

invocation:

$ awk -f a1.awk

Page 22: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Arrays - Sparse

Vectors can be sparseIndices can even be negativeUnitialised indices evaluate to 0 or "", depending oncontext

sparse.awk

BEGIN {a[5] = "kurt"a[12] = 13a[13] = "Ski"a[-77] = "I’m here, too"for( k in a )

print k, a[k]print "a[7] =", "" a[7]print "a[7]+5 =", a[7]+5

}

output:

5 kurt12 1313 Ski-77 I’m here, tooa[7] =a[7]+5 = 5

Page 23: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Arrays - Associative

Remember, they’re all associative arraysIndices can be numbers or strings

In fact, they’re all strings

tally.awk

{ tally[ $1 ] += $2 }

END {for( n in tally )

print n, tally[n]}

output:

$ awk -F’,’ -f tally.awk < tally.sampleMorgan 27Marek 162Sean 64Hannah 55

tally.simple:

Hannah,6Sean,38Marek,40Hannah,40Marek,36Marek,37Sean,26Hannah,9Morgan,27Marek,49

Page 24: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Arrays - More

delete removes an array entrydelete a[3]

AWK supports multidimensional arraysa[i,j] = i*j

On a simple arraySubscripts are concatenated

Gawk supports arrays of arrays:a[i][j] = i*j

Page 25: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Sorting Arrays

Gawk provides sorting functions for arrays:

asort( src [, dest] )asorti( src [, dest] )

asort – Sorts the valuesasorti – Sorts the indices (keys)Returns the number of elementsDestroys indices

Enumerates from 1

Page 26: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Arrays – asort

sort.awk

BEGIN {IGNORECASE = 0 + ics = "shamrock bog clock craic Sidhe taisca eejit gob"split( s, a )n = asort( a )for( i=1; i<=n; ++i )

print i, a[i]}

output:

$ awk -f sort.awk1 Sidhe2 bog3 clock4 craic5 eejit6 gob7 shamrock8 taisca

Page 27: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Sorting – IGNORECASE

sort.awk

BEGIN {IGNORECASE = 0 + ics = "shamrock bog clock craic Sidhe taisca eejit gob"split( s, a )n = asort( a )for( i=1; i<=n; ++i )

print i, a[i]}

output:

$ awk -v ic=1 -f sort.awk1 bog2 clock3 craic4 eejit5 gob6 shamrock7 Sidhe8 taisca

Page 28: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Numeric Sorting

There are a number of predefined predicates forPROCINFO["sorted_in"], or you can define your own.

iSort.awk

BEGIN { PROCINFO["sorted_in"] = val_num_asc }{ a[NR] = 0 + $1 } # make it a numberEND { asort( a ) ; for( i in a ) print a[i] }

iSort.in:

662813763147559

output:

$ awk -f iSort.awk iSort.in413283159667576

Page 29: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Sorting Non-destructively

Remember, the original indices are lostasort takes an optional destination arraySorts into this array, leaving original untouched

iSort.awk

{ a[$1] = $2 }END {

n = asort( a, b )print "Original array:"for( k in a )

print k, a[k]print "\nSorted values:"for( i=1; i<=n; ++i )

print b[i]}

Page 30: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Sorted Keys – asorti

Use asorti to sort the keys (indices) into another array1:

sorti.awk

{ a[$1] = $2 }

END {n = asorti( a, keys )for( i=1; i<=n; ++i )

printf( "%10s : %s\n", keys[i], a[keys[i]] )}

2-cols.in:

Sam,Into the MysticRoy,GambolUri,Wine DownElisabeth,Bay PoetBruce,Legacy

output:

$ awk -F’,’ -fsorti.awk < 2-cols.inBruce : Legacy

Elisabeth : Bay PoetRoy : GambolSam : Into the MysticUri : Wine Down

1Not all AWKs, I think. You can write your own.

Page 31: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Defining Functions

Introduced with keyword function

function func_name([param_list]){

body}

Parameters may not have same name as built-invariablesParameters may not have same name as functionParameter list contains arguments and local variables

Parameters not assigned are local variables, defaultingto the empty stringVariables in body not in parameter list are global

Page 32: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Functions – Example

func.awk

function foo( x, i ){

i = 12print "You passed in:", xj = "foo’s j"k = "foo’s k"

}

BEGIN {i = 5 # Also globalj = "global"foo( "Heather" )print "i is:", iprint "j is:", jprint "k is:", k

}

output:

$ awk -f func.awkYou passed in: Heatheri is: 5j is: foo’s jk is: foo’s k

Page 33: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

Functions – Example w/return

catmult.awk

function catmult( s, n ){

rv = sfor( i=1; i<n; ++i )

rv = rv(s)

return rv}

BEGIN {s = catmult( "Heather", 3 )print "s is:", s

}

output:

$ awk -f catmult.awks is: HeatherHeatherHeather

Page 34: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

One-Liners

Page 35: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

AWK One-Liners

Line count$ awk ’END {print NR}’

Like grep$ awk ’/regex/’

Like head$ awk ’FNR<=10’

Add line numbers$ awk ’{print FNR, $0}’$ awk ’{printf( "%03d %s\n", FNR, $0 )}’

Print lines 12-23, inclusive$ awk ’FNR==12,FNR=23’

Page 36: AWK – Introduction AWK – Introductionkschmidt/CS265/Lectures/Awk/awk.pdf · AWK – Introduction Kurt Schmidt Intro Invocation AWK Programs Patterns Actions AWK Language Fields

AWK –Introduction

Kurt Schmidt

IntroInvocation

AWKProgramsPatterns

Actions

AWKLanguageFields

Variables

Numbers

Strings

Arrays

Sorting

Functions

One-Liners

More One-Liners

Remove blank lines1

$ awk ’/./’$ awk ’NF>0’

Double-space a file

$ awk ’1;{print ""}’ # 2 separate rules$ awk ’BEGIN{ORS="\n\n"};1’ # Also 2 rules

Smarter double-space

$ awk ’NF>0 {print $0 "\n"}’

Remove leading whitespace from each line

$ awk ’{sub(/^[ \t]+$/, "")};1’ # Again, 2 rules

1Mind parsing DOS files. \n is preceded by \r


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The awk programming_language

Awk- An Advanced Filter Introduction Simple awk Filtering · 2017-03-31 · Awk- An Advanced Filter Introduction awk is a programmable, pattern-matching, and processing tool available

Tools for processing text: awk - Santa Monica Collegehomepage.smc.edu/.../linux/a05ss-04-InteractiveBash-text-tools_awk.pdf · Tools for processing text: awk David Morgan awk scripts

The AWK Pattern Processing Language - cdn.ttgtmedia.com · AWK has many implementations tip The AWK language was originally implemented under UNIX as the awk utility. Most Linux distri-butions

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1 1: awk 2 - RIP Tutorial · 2019. 1. 18. · 1: awk AWKAlfred V. AhoPeter J. Weinberger Brian W. Kernighan。 • Illumos AWK • Plan9 AWK • GNU AWK • AWK POSIX awk 1992 IEEE

The AWK Manual - Freecyrille.nathalie.free.fr/pages/linux/awk.pdf · This is Edition 1.0 of The AWK Manual, for the new implementation of AWK (sometimes called nawk). Notice: This

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Introduction to awk programming - michael-herbst.com€¦ · $ awk ' /hunger/' resources/gutenberg/pg76.txt and $ awk ' /hunger/' resources/gutenberg/pg74.txt One solution for the

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AWK – eine fast vergessene Programmiersprache · 2020. 10. 9. · AWK - Eigenschaften AWK-Varianten •oawk– Erste Version ab 1977 (old AWK) •nawk– Erweiterte Version ab 1985

1 Xiaolan Zhang Spring 2013 CISC3130: awk. 2 Outlines Overview awk command line awk program model: record & field, pattern/action pair awk program elements:

Versions/Implementations awk : original awk nawk : new awk, dates to 1987 gawk : GNU awk has more powerful string functionality - NOTE – We are going

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