4.Brief commands overview

The language looks a little like C but automatically handles input, field splitting, initialization, and memory management.

Built-in string and number data types
No variable type declarations

data[1]= 330                   
data[3]= "text"     # yes, the elements could be of different type
data[7]= 7.5                   
data["Monday"]= 1

awk is a great prototyping language

start with a few lines and keep adding until it does what you want

awk gets its input from

files
redirection and pipes
directly from standard input

Exercise

Let's start with something simple Exercises/01.Simple arithmetic.

Common commands and constructions - examples

Loop

for (i=1; i<=10; i++) {
  print i
}

Exercise

Let's try to use loops for some simple tasks Exercises/05.Easy_tricks

If else statement

if ($1 > 2) {
  print $2 
} else if ($1 < 2) {
  print $3 
} else {
  print $3 
}

Exercises

time to add a bit more, so we can get some meaningful calculations on our data Exercises/Warming up.

While statement

while ($1 < $3) {
  getline; print
}

Other

print "Text"$1"more text"

printf ("Text %g more text", $1)

next    #  (skips the remaining patterns on the current line of input)

exit    #  (skips the rest of the current line)

Exercises

Let's see how can we format better the output of an awk script Exercises/String manipulation
At this point, we should be abe to decipher Multiline Fasta To Single Line Fasta.

Predefined variables

NR - Number of records processed
FNR - Number of record processed in the current file while NR refers to the total record number. For the first file FNR==NR, but for the second FNR will restart from 1 while NR will continue to increment.
NF - Number of fields in current record
FILENAME - name of current input file
FS - Field separator, space or TAB by default
OFS - Output field separator, space by default
ARGC/ARGV - Argument Count, Argument Value array - get arguments from the command line

$1 - first field value, $2 - second etc.

$0 - contains the entire line

Built-in functions

Arithmetic

sin(), cos(), atan(), exp(), int(), log(), rand(), sqrt()

String manipulation functions

length(), substitution, find substrings, split strings

Output

print, printf(), print and printf to file

Special

system() - executes a Unix command e.g., system("date") to execute "date" command. Note double quotes around the Unix command

If you have reached this point, perhaps you are already asking where you can read something to begin with. This site is perhaps good for beginners: https://en.wikibooks.org/wiki/AWK