SOME COMMON AWK COMMANDS
print the content of the file using awk
awk ‘{print}' filename.txt
Adding a new line of word at top of the file
awk ‘BEGIN{printf "This is new line"}{print}’ filename.txt
Assigning a value to the variable before execution
awk -v name="Jack" ‘BEGIN{printf "Name = $s\n", name}’
Print a specific column or field of the file
awk ‘BEGIN{FS=" "}{print $3 "\t" $4}' filename.txt
For reference this is the text file we will be using:
1) Amit Physics 80
2) Rahul Maths 90
3) Shyam Biology 87
4) Kedar English 85
5) Hari History 89
Lets name it marks.txt — — →
print the line matching the pattern —
awk ‘/a/ {print $0}’marks.txt
This will print all line with a in it. For instance, in the file above it will print line 2,3,4,5
If some specific field or column of the matched line is required then it can be done in the similar fashion as for the normal awk withou matching regex
awk ‘/a/ {print $2 "\t" $3}' marks.txt
Similarly all the other patterns can be checked for its existence in the sentence.
Similarly we can find the count of the line containing a in the file.
awk ‘/a/ {++cnt} END {print "Count =" cnt}' marks.txt
Print lines with more than n(here 18) characters
awk ‘length($0) > 18' marks.txt
Standard AWK variables
awk ‘BEGIN{print "Commands=" ARGC}’ one two three four
This prints command = 5
ARGC, calculates he the no of lines commands available, Here[ awk,one,two,three,four]
User→ FS for file seperator
awk ‘BEGIN{FS=" " }’ marks.txt
We can get the number of fields in the column using NF command
awk ‘NF > 2’marks.txt
print all the lines with more than two fields
NR represents the number of present record
awk ‘NR < 3’ marks.txt
This will print the first two lines of the file
Similarly,
Output field Seperator(OFS)
awk ‘BEGIN{OFS=”|”}{print $1,$2}’
Similarly, we can set Output Row Seperator (ORS), by default the ORS is “\n”, But can be change as per requirement, for instance:
wk ‘BEGIN{ORS=”-”}{print $0}’ marks.txt
1) Amit Physics 80–2) Rahul Maths 90–3) Shyam Biology 87–4) Kedar English 85–5) Hari History 89-
The output row is seperated by “-”
match and RLENGTH
match checks if a particular substring is present in the string or not.
RLENGTH prints the length of the matched string
awk ‘BEGIN{FS=" "}{if (match($3,"Ph")){print $2}} marks.txt’`
This will print 2 as output
RSTART → This gives the position of the first match in the string
awk ‘BEGIN{FS=” “}{if (match($3,”Ph”)){print RSTART}}’ marks.txt
IGNORECASE → Search for a substring ignoring case
awk ‘BEGIN{IGNORECASE=1} /amit/’ marks.txt
1) Amit Physics 80
Arithematic Operator
awk ‘BEGIN{a=2; b=3; print “SUM=”,a+b;print “SUBS=”,a-b;print “MUL=”,a*b;print “DIV=”,a/b;print “MODULUS=a%b”;}’
SUM= 5
SUBS= -1
MUL= 6
DIV= 0.666667
MODULUS=a
Increment and Decrement Operator
awk ‘BEGIN{a=5; print a++; print a;}’
The increment and decrement operator works in the similar fashion as the programming of C or Java. Above is one such illustration.
Assignment Operator and Shorthands
assignment: → =
addition shorthand: → a += b — — → a = a + b
multiplication → a*= b
divison → a/=b
exponential: → a^=b or a**=b
Relational Operator
The signs are same as of C,C++ or Java
Logical operator are also the same
Exponential Operator
^,**
String concatenation operator
space is used for string concatentaion
awk ‘BEGIN{a="Hello ";b="World";print a b}’
will print Hello World`
Array Membership operator
awk 'BEGIN {
arr[0] = 1; arr[1] = 2; arr[2] = 3; for (i in arr) printf "arr[%d] = %d\n", i, arr[i]
}'Regular Expression Operator
Match
It is represented as ~. It looks for a field that contains the match string. For instance, the following example prints the lines that contain the pattern 9.
Example
[jerry]$ awk '$0 ~ 9' marks.txtOn executing this code, you get the following result −
Output
2) Rahul Maths 90
5) Hari History 89Not Match
It is represented as !~. It looks for a field that does not contain the match string. For instance, the following example prints the lines that do not contain the pattern 9.
Example
[jerry]$ awk '$0 !~ 9' marks.txtOn executing this code, you get the following result −
Output
1) Amit Physics 80
3) Shyam Biology 87
4) Kedar English 85Arrays in AWK
array_name[“index_name”] = value
Deleting an array element
delete array_name[“index_name”]
Next like all other programming language awk also got work flow. So now lets us explore the work flow with example:
AWK have if-else if -else conditional operation, it has for, while and do while like c, similarly ith has case operation like c
IF
e.g →
awk ‘BEGIN{FS=" ";count=0}{if($3 > 50){count++;}} END {print count}’
The above program will count all occurence of $3>50 and will print accordingly.
Similarly, else — if ladder can be formed lets see it how.
awk ‘BEGIN{FS=" ";count=0;count1=0}{if($3 ==50){count++;}else if($3 == 60){count1++;}else{print "Not counting";}} END {print count "\n" count1;}
In the above code, whenever 50 is found the count increases and similarly when 60 found count1 increases. and similarly adder continues as clear from the example.
FOR
awk ‘BEGIN{FS=" ";OFS=" ";i=0}{arr[i++]=$3} END {for(j=0;j<i;j++){for(k=0;k<i-j-1;k++){if(arr[k] > arr[k+1]){temp = arr[k];arr[k] = arr[k+1];arr[k+1]=temp;}}} for(j=0;j<i;j++){print arr[j]}}’`
The above program is a bubble sort illustrating foe loop in awk. In the first step we build up array by fetching data from the file. Next we ran for loop in the same fashion as we run in c,c++ or java to get our work done.
WHILE
The format of while also is same as in c or java. Lets see how:
awk ‘BEGIN{FS=" ";count=0;i=0}{while(i<=4){count = count + 1;i++;}} END {print count;}’`
This is a program illustrating the use how to use count using while loop. Similarly do — while can be performed. The skeleton of do while is shown below:
do{some_action}while(certain_condition_reached)
That’s it, I think we are done playing syntax and illustration regarding awk. For further practice I would suggest you using hacker rank platform.
Inside HackerRank search for → UNIX and pratice questions of awk over there. This will broaden your concept.
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