an awk-ward (or not really) language.

some notes in process.

projects

g2e is an opinionated gempub to epub converter written in awk:

g2e

my solutions for advent of code 2021 have been written in awk.

resources

gawk user's guide

awk tutorial: tutorialspoint

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)
• RSTART: index of the first position in the string matched by match( )
• RLENGTH: length of the string matched by match( )
• ARGV: array that stores the command-line arguments. index starts at 0
• ARGC: number of command-line provided arguments
• ARGIND: index in ARGV that is currently being processed (not necessarily compatible with all awks)

$0 represents the entire input record, and $n the nth field in the current record (starting to count from 1)

awk tutorial: built-in variables

some built-in functions

awk tutorial: built-in functions

miscellaneous functions

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 separator
• 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. and other possibilities:

Explicit Input with getline

The getline command is used in several different ways and should not be used by beginners.

(?)

• 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

gawk

gawk user's guide

bit-manipulation functions

note: to run in compatibility mode, without gnu extensions, use the -c or --traditional flag:

$ awk -c

other notes

• apparently counters/accumulators don't need to be initialized at 0
• boolean values are 0 or 1

record separation

records separated by empty lines can be extracted with:

RS = ""

without modifying FS, fields will be separated by any whitespace, including newlines.

gawk allows regexp in RS, traditional awk will only accept one character.

field separation

one can get one character at a time by setting (in gawk?) :

FS = ""

loop through the elements of an array

this approach might yield the results in different order depending on the awk implementation.

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

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