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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.

Syntax

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

Program Structure

BEGIN Block

BEGIN {awk-commands}

BODY Block

/pattern/ {awk-commands}

END Block

END {awk-commands}

Important Flags

FlagsDescription

-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

Built in Variables

VariableDescriptionExample

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

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

CharacterPrints 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

CommandOutput
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 "%%"

%

Examples

CommandDescription
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

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