Awk notes, awk learning notes

Awk notes, awk learning notes
Awk:

• Awk names: The abbreviations of the three people: Aho, (Peter) weberger and (Brain) Kernighan;
• In-row fields can be processed during row processing. This is not allowed by grep/sed. In special cases, $0 is used to indicate the row;
• Usage: awk [-F re] [parameter...] ['prog'] [-f progfile] [in_file...]
  • -F column separator;
  • Prog: 'pattern' {action} '. pattern is a specific string and supports regular expressions, such as cat uids | awk'/[0-9] + \. [0-9] */{print }';
  • -F: a script file that complies with the awk syntax;
  • In_file: input file. Multiple Input files are allowed ;???
• Pattern character representation:
  • \ Code change sequence
  • ^ Start matching at the beginning of the string
  • $ Start matching at the end of the string
  • . Match with any single string
  • [ABC] matches any character in []
  • [A-Ca-c] matches characters in the A-C and a-c range (in alphabetical order)
  • [^ ABC] matches any character other than all characters in [].
  • Desk | Chair matches any one of Desk and Chair
  • [ABC] [DEF] Association. Matches any character in A, B, and C, and must be followed by any character in D, E, and F.
  • [ABC] * matches any character in A, B, or C that appears 0 or multiple times
  • [ABC] + matches any one or more characters in A, B, or C.
  • ? Matches an empty string or A, B, or C in any character
  • (Blue | Black) the regular expression of berry merging, which matches with Blueberry or Blackberry.
• Arithmetic Operators:
  • Y Power of x ^ y x
  • X ** y same as above
  • X % y calculate the remainder of x/y (Modulo)
  • X + y
  • X-y x minus y
  • X * y x multiplied by y
  • X/y x except y
  • -Y negative y (the switch symbol of y); also known as one minus
    + + Y + 1 and then use y (prefix)
  • Add 1 (suffix ),
  • -- Y minus 1 and use y (minus)
  • Y -- after use, y minus 1 (suffix minus)
  • X = y: Assign the value of y to x.
  • X + = y: Assign the value of x + y to x.
  • X-= y: Assign the value of x-y to x.
  • X * = y: Assign the value of x * y to x.
  • X/= y: Assign the value of x/y to x.
  • X % = y: Assign the value of x % y to x
  • X ^ = y: Assign the value of x ^ y to x
  • X ** = y: Assign the value of x ** y to x.
    
• Logical operators:
  • X = y
  • X! = Y
  • X> y
  • X> = y
  • X <y
  • X <= y
  • X ~ Re
  • X !~ Re
• Built-in variables:
  • ARGC: Number of command line parameters.
  • ARGIND: the location of the current file in the command line (starting from 0 ).
  • ARGV: An array containing command line parameters.
  • CONVFMT: Numeric conversion format (default value: %. 6g)
  • ENVIRON: environment variable associated array.
  • ERRNO: Description of the last system error.
  • FIELDWIDTHS: field width list (separated by Space key ).
  • FILENAME: The current file name.
  • FNR: Same as NR, but relative to the current file.
  • FS: Field separator (any space by default ).
  • IGNORECASE: if it is true, case-insensitive matching is performed.
  • NF: number of fields in the current record.
  • NR: Number of current records.
  • OFMT: Number output format (default value: %. 6g ).
  • OFS: delimiter of the output field (the default value is a space ).
  • ORSL: Output record delimiter (default value is a line break ).
  • RLENGTH: the length of the string matched by the match function.
  • RS: Record separator (a line break by default ).
  • RSTART: the first position of the string matched by the match function.
  • SUBSEP: array subscript separator (default value: \ 034)
• Built-in functions: Class C style usage;
  • Printf: format the output, such as awk '{printf "% 03d % s \ n", NR, $1}' myfile
    
  • N gsub (reg, string, target) replaces the string
  • N index (search, string) returns the position of the search string in string
  • A length (string) calculates the number of characters in the string.
  • N match (string, reg) returns the position in the string matching the regular expression reg
  • N printf (format, variable) formats the output, and outputs the variable in the format provided by format.
  • N split (string, store, delim) Splits string into store array elements based on delim.
  • N sprintf (format, variable) returns a format-based formatted data. variables is the data to be placed in the string.
  • G strftime (format, timestamp) returns a date or time String Based on format. timestmp is the time returned by the systime () function.
  • The first time that N sub (reg, string, target) matches a regular expression reg, it replaces the string in the target string.
  • A substr (string, position, len) returns A substring starting with position len
  • P tolower (string) returns the lowercase characters in string.
  • P toupper (string) returns the uppercase characters in string.
  • Cotangent (radians) of A atan (x, y) x)
  • Cosine (radian) of N cos (x) x)
  • X power of A exp (x) e
  • Integer part of A int (x) x
  • Natural logarithm of A log (x) x
  • Random Number between N rand () 0-1
  • Sine (radian) of N sin (x) x)
  • Square root of A sqrt (x) x
  • A srand (x) initializes the random number generator. If x is ignored, system () is used ()
  • G system () returns the time elapsed since January 1, January 1, 1970 (in seconds)
• Process control:
  • Logical operators :......
  • BEGIN/END:
  • If-else:
  • While/do-while//
  • Break/continue/exit (exit but do not skip END)
  • Next: Read the next record;
• Content Control:
  • Read File: getline
  • Close file: close, which can be opened for getline files;
  • Export File: printf ("hello word! \ N ")>" datafile"
  • Export to other commands: printf ("hello word! \ N ") |" sort-t ','"
  • Read Other command results: who-u | awk '{printf ("% s is executing % s \ n", $2, $1 )}'
  • Run shell command line in awk: Embedded function system (). The parameters passed to this function are considered as command execution: END {close ("myreport.txt "); system ("lp myreport.txt ");}
• Example:
  • Show text 7th ~ Row 15: awk-F % 'nr = 7, NR = 15 {printf $1 $3 $7 }'
  • 
    
• Tips or note:
  • 1. If you want to explicitly type the variables used by the awk, you should assign the initial value to it in the program; if the awk does not know, the default string type is used;
  • 2. If a column is read as a numeric value and a numeric value is processed, awk treats it as 0 if the column is not a legal number;
  • 3 for (x in myarray) when printing an array, the output may be out of order;
  • 4 if (1 in fooarray), does the array contain this value ???? It seems to be ineffective.
  • 5