# awk

an awk-ward (or not really) language.

some notes in process.

# some built-in variables

* FS: input field separator (by default, space)
* RS: record field separator (by default, newline)
* NF: number of fields in current record
* NR: number of current record
* FNR: number of current record relative to current file
* OFS: output field separator (by default, space)
* ORS: output record separator (by default, newline)
* RLENGTH: length of the string matched by match( )

$0 represents the entire input record, and $n the nth field in the current record

=> https://www.tutorialspoint.com/awk/awk_built_in_variables.htm awk tutorial: built-in variables

# some built-in functions


=> https://www.tutorialspoint.com/awk/awk_built_in_functions.htm awk tutorial: built-in functions
=> https://www.tutorialspoint.com/awk/awk_miscellaneous_functions.htm miscellaneous functions
=> https://www.tutorialspoint.com/awk/awk_string_functions.htm string functions

## strings

the index of the first character is 1!

* index( string, sub) : index of sub as a substring of string
* length( string )
* match( string, regex ) : index of the longest match of regex in string
* split( string, arr, regex ) : split string into array using regex as separato
* printf( format, expr-list)
* strtonum(string): useful to convert from hexadecimal (0x prefix) or octal (0 prefix)
* gsub( regex, sub, string): global substitution of regex with sub in string. if string is ommited, $0 is used
* sub(regex, sub, string): substitute regex with sub in string, once. if string is omitted, $0 is used
* substr(string, start, len): returns the substring from start index, with length len. if len is ommitted, it goes until the end of the string
* tolower( str )
* toupper( str )

## misc

* getline: read the next line
* next: stops the current processing and start over with next line
* system: execute the specified command and returns its exit status
* delete: delete an element from an array, or an array

# other notes

## loop through the elements of an array

```
arr["a"] = 1
arr["b"] = 2

for(key in arr)
  print key ": " arr[key]
```