awk

awk linux command cheatsheet by Thamizhiniyan C S

Introduction

Awk is a scripting language used for manipulating data and generating reports.The awk command programming language requires no compiling, and allows the user to use variables, numeric functions, string functions, and logical operators.

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Syntax

awk [flags] [select pattern/find(sort)/commands] [input file]

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Program Structure

BEGIN Block

Awk

BEGIN {awk-commands}

BODY Block

Awk

/pattern/ {awk-commands}

END Block

Awk

END {awk-commands}

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Important Flags

Flags	Description
-F	With this flag you can specify FIELD SEPARATOR (FS), and thus don't need to use the BEGIN
-v	Can be used to specify variables(like we did in BEGIN{OFS=":"})
-D	You can debug your .awk scripts specifying this flag(awk -D script.awk)
-o	To specify the output file (if no name is given after the flag, the output is defaulted to awkprof.out)
f	Reads the AWK program source from the file program-file, instead of from the first command line argument
--dump-variables	Prints a sorted list of global variables and their final values to file

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Built in Variables

Variable	Description	Example
ARGC	It implies the number of arguments provided at the command line	awk 'BEGIN {print "Arguments =", ARGC}' One Two Three Four
ARGV	It is an array that stores the command-line arguments. The array's valid index ranges from 0 to ARGC-1	awk 'BEGIN { for (i = 0; i < ARGC - 1; ++i) { printf "ARGV[%d] = %s\n", i, ARGV[i] } }' one two three four
CONVFMT	It represents the conversion format for numbers. Its default value is %.6g	awk 'BEGIN { print "Conversion Format =", CONVFMT }'
ENVIRON	It is an associative array of environment variables	awk 'BEGIN { print ENVIRON["USER"] }
FILENAME	It represents the current file name	awk 'END {print FILENAME}' marks.txt
FS	It represents the (input) field separator and its default value is space	awk 'BEGIN {print "FS = " FS}' | cat -vte
NF	It represents the number of fields in the current record	echo -e "One Two\nOne Two Three\nOne Two Three Four" | awk 'NF > 2'
NR	It represents the number of the current record	echo -e "One Two\nOne Two Three\nOne Two Three Four" | awk 'NR < 3'
FNR	It is similar to NR, but relative to the current file	-
OFMT	It represents the output format number and its default value is %.6g	awk 'BEGIN {print "OFMT = " OFMT}'
OFS	It represents the output field separator and its default value is space	awk 'BEGIN {print "OFS = " OFS}' | cat -vte
ORS	It represents the output record separator and its default value is newline	awk 'BEGIN {print "ORS = " ORS}' | cat -vte
RLENGTH	It represents the length of the string matched by match function	awk 'BEGIN { if (match("One Two Three", "re")) { print RLENGTH } }'
RS	It represents (input) record separator and its default value is newline	awk 'BEGIN {print "RS = " RS}' | cat -vte
RSTART	It represents the first position in the string matched by match function	awk 'BEGIN { if (match("One Two Three", "Thre")) { print RSTART } }'
SUBSEP	It represents the separator character for array subscripts and its default value is \034	awk 'BEGIN { print "SUBSEP = " SUBSEP }' | cat -vte
$0	It represents the entire input record	awk '{print $0}' marks.txt
$n	It represents the nth field in the current record where the fields are separated by FS	awk '{print $3 "\t" $4}' marks.txt

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printf statement

awk's printf statement is the same as that in C, except that the * format specifier is not supported.

SYNTAX: printf format, expr1, expr2, ..., exprn

awk printf conversion characters

Character	Prints expression as
%c	single character
%d	decimal integer
%e	[-]d.dprecisionE[+-]dd
%f	[-]ddd.dprecision
%g	e or f conversion, whichever is shorter, with nonsignificant zeros suppressed
%o	unsigned octal number
%s	string
%x	unsigned hexadecimal number
%%	print a %; no argument is converted

printf examples

Command	Output
printf "%d", 99/2	49
printf "%e", 99/2	4.950000e+01
printf "%f", 99/2	49.500000
printf "%6.2f", 99/2	49.50
printf "%g", 99/2	49.5
printf "%o", 99/2	61
printf "%06o", 99/2	000061
printf "%x", 99/2	31
printf "|%s|", "January"	|January|
printf "|%10s|", "January"	| January|
printf "|%-10s|", "January"	|January |
printf "|%.3s|", "January"	|Jan|
printf "|%10.3s|", "January"	| Jan|
printf "|%-10.3s|", "January"	|Jan |
printf "%%"	%

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Examples

Command	Description
awk '{print}' file.txt	To simply print a file
awk '/ctf/' file.txt	To search for a pattern inside a file
awk '{print $1,$3}' file.txt	To list the words that are at 1st and 3rd fields
awk '{print NR,$0}'	To number the lines
awk 'BEGIN {FS="o"} {print $2}' file.txt	Split based on the character 'o'
awk "BEGIN {FS='o'} {print $1,$3} END{print 'Total Rows=',NR}"	Split with the character 'o' and print the total number of characters
awk 'BEGIN {RS="o"} {print $0}' file.txt	Separate rows base with 'o'
awk 'BEGIN {OFS=":"} {print $1,$2,$3,$4}' file.txt	To specify field delimeter while outputing
awk 'BEGIN {ORS=":"} {print $0}' file.txt	To specify record delimeter while outputing
awk '!($2 && $3 && $4) {print "Not all scores are available for " $1}'	Checks if fields 2, 3, and 4 are all empty. If they are, it prints a message indicating that not all scores are available for the item identified in the first field
awk '{ if ( $2 == "" || $3 == "" || $4 == "" ) { print "Not all scores are available for", $1; } }'	Checks if fields 2, 3, and 4 are all empty. If they are, it prints a message indicating that not all scores are available for the item identified in the first field
awk '{ grade="Pass" if ( $2<50 || $3<50 || $4<50) grade="Fail" print $1,":",grade }'	Evaluates student scores and assigns a grade of "Pass" or "Fail" based on whether any of their scores are below 50. It then prints the student identifier along with their grade
awk '{ average = ( $2 + $3 + $4 ) / 3 if ( average >= 80 ) print $0, ":", "A" else if ( average >= 60 ) print $0, ":", "B" else if ( average >= 50 ) print $0, ":", "C" else print $0, ":", "FAIL" }'	To identify the performance grade for each student. If the average of the three scores is 80 or more, the grade is 'A'. If the average is 60 or above, but less than 80, the grade is 'B'. If the average is 50 or above, but less than 60, the grade is 'C'. Otherwise the grade is 'FAIL'.
awk '{ printf ($0) if ( NR % 2 == 0 ) printf "\n" else printf ";" }'	Formats input data by printing each line as is, but inserts a newline character every two lines and a semicolon after every odd-numbered line. This formatting creates a specific structure in the output