AWK Examples and Help

   AWK INTRO

Usage:- # awk '{instructions}' file(s)
 
# awk '/pattern/ {procedure }' file
# awk -f script_file(s)

Tasks:
 
1. print entire row, one at a time from an input file
 Note: $0 represents the current record or row
  
   a. # awk '{ print $0 }' animals.txt
  
2. Print specific colums from animals.txt
 
# awk '{ print $1 }' animals.txt --- prints the firest colums from the file
    awk '{ print $2 }' animals.txt
If we change column from 1 to 2 we can print elements of second column 

even blank space as well.

3. Print multiple colums from animals.txt
    awk '{ print $1; print $2; }' animals.txt
    awk '{ print $1, print $2; }' animals.txt
    awk '{ print $1,$2; }' animals.txt   ---------- If there is no delemeters in the
  file(only space) we can give like this

awk -F: '{ print $1; print $2; }' /etc/passwd    ------- if any delemeter is there better give '-F' option.
 
awk -F: '{ print $1, $2; }' /etc/passwd   

4. Print columns from lines containing 'deer' --- pattern
  a. awk '/deer/ { print $0 }' animals.txt
 
5. Prints columns from lines containing digits
  a. awk '/[0-9]]/ { print $0 }' animals.txt
     dog1
     deer200
   regular expresion search [0-9]

6. Print lines begunning with numeric characters
    a. awk '/^[0-9]]/ { print $0 }' animals.txt
        123lion
         7
6. Print lines begunning with Multiple characters
     a. awk '/^[0-9]]*$/ { print $0 }' animals.txt
7. Remove blank lines using sed and pipe output to awk for processing   
 # sed -e /^$/d animals.txt | awk '/^[0-9]]*$/ { print $0 }'

In awk if we dont specify any pattern it will operate on every line, if we specify the pattern it will operate on that specific line or lines.

awk '/^$/ { print $0 }' animals.txt --- print all blank lines.

 Case insensitve and Case sensitve etc are same as sed


   Delimiters

Default Delimiter: whitespace {space, tabs}
Use: '-F' to influence the default delimiter

awk -F: '{ print $1; print $2; }' /etc/passwd ---- It will print the dats in seperate lines
awk -F: '{ print $1, $2; }' /etc/passwd --- It will print the datas in single line.

   awk Scripts

organize patterns and procedures into a script file
Loops through lines of input from various sources: STDIN, Pipe, Files

Tasks:
1.Print something to the screen without reading input
a. # awk 'BEGIN { print "testing awk without input file" } '

2. set system: Field seperator to colon in BEGIN block
  a. awk 'BEGIN { FS = ":" } '
  b. awk 'BEGIN { FS = ":" ; print "testing awk without input file" } '
      Here seperating FS(field seperator and print using "semi-colon" (;). We can use multiple print statement using seperaate them by using semi-colon(;)

  c. awk 'BEGIN { FS = ":" ; print "testing awk without input file"; print FS } '
 
Task: Print the line which containing the work deer from animals.txt
# awk script to find deer

# Component 1 - BEGIN
BEGIN { print " processing various records" }

# Component 2 - Main Loop
/deer/ { print }  ----- this reads as "if the line containing deer, print the line"

# Component 3 - END
END { print "process complete"

  in this script first two components are optional, only main loop is enough for executing it.

  here saved file as animals.awk and then run the awk script
 
# awk -f animals.awk animals.txt

Task: parse /etc/passwd
Print entire line

# Component 1 - BEGIN
BEGIN { FS = ":" print " processing various records" }

# Component 2 - Main Loop
 { print }  ----- this will simply print the entire lines

# Component 3 - END
END { print "process complete"

saved it as test.awk

# awk -f test.awk /etc/passwd

Task: To print the specific name or colum from /etc/passwd

# Component 1 - BEGIN
BEGIN { FS = ":" print " processing various records" }

# Component 2 - Main Loop
 { print $1, $5 }  ---- print specific columns

# Component 3 - END
END { print "process complete"

Taks: Print specific columns for a specific user: /linuxcbt/ { print $1, $5 }

# Component 1 - BEGIN
BEGIN { FS = ":" print " processing various records" }

# Component 2 - Main Loop
 /linuxcbt/ { print $1, $5 }  ---- Print specific columns for a specific user

# Component 3 - END
END { print "process complete"

# awk -f test.awk /etc/passwd

Taks: Print specific coloms for a specific user matching a given column: $1 ~ /name/ { print $1, $5 }
column number 1 followed by tild and value containing column number 1

Taks: print all users who contains shell "bash"
# Component 1 - BEGIN
BEGIN { FS = ":" print " processing various records" }

# Component 2 - Main Loop
$7 ~ /bash/ { print }  ---- Print specific columns for a specific user

# Component 3 - END
END { print "process complete"

# awk -f test.awk /etc/passwd

  AWK Variables
 
Three Types:-

1.System Variables  -- FileName,RS(Record Seperator)
2.Scalars ---- ie, a = 3
3.Arrays -- ie, variable_name

NOTE:- Variables do not need to be declared. AWK automatically rgisters them in memory.
NOTE:- Variable names are case sensitive

 System Variables:
1. FILENAME: Name of current input file
2. FNR : used when multiple input files are used
3. FS or Field seperator : defaults to whitespaces - can be a single character, including via RegEx
4. OFS : Output field seperator
5. NF: Number of fields in current records

# Component 1 - BEGIN
BEGIN { print " processing various records" }

# Component 2 - Main Loop
/deer/ { print }  ----- this reads as "if the line containing deer, print the line"
{ print NF }
# Component 3 - END
END { print "process complete"
print "Filename: " FILENAME

   AWK Process Records

Processing multiple delemeters in the same file
awk -F "[:; ]" '{print }' animal2.txt
awk -F "[:; ]" '{print $1 }' animal2.txt
awk -F "[:; ]" '{print $1,$2 }' animal2.txt