AWK

#!/usr/bin/awk -f
END { print "Hello, World!"; }

• Authors
  • Aho Alfred Vaino
  • Weinberger Peter Jay
  • Kernighan Brian Wilson
• 2023
  • –csv, supports fields surrounded by double quotes
• https://www.gnu.org/software/gawk/manual/html_node/Conversion gawk always uses the period (.) as the decimal point unless told explicitly to use the local LC_NUMERIC –posix –use-lc-numeric (-N)

• sometimes not enforcing variables to be local can cause weird issues. early return, should happen as soon as possible otherwise this function will keep looping… If I move the if/return0 to the top it works just fine OR if I make "middle" a local variable

  function binarySearch(target,    left, right) {
      middle = int((left+right)/2)
      print "l:", left, "r:", right, "m:", middle, "n[m]="numbers[middle]
      if (left >= right) {
          return 0
      }
      if (numbers[middle] > target) binarySearch(target, left, middle-1)
      if (numbers[middle] < target) binarySearch(target, middle+1, right)
      return numbers[middle] == target
  }
  

• length($0) = 0 { print "this is an empty record=" } END { if (NR == 0) print "means that we didn't process any record" }
• || and && return booleans. AKA 0 or 1. They do NOT return the truthy value.
• Can redefine NF=0 at END and then add new $(++NF)=??? to later just print
• falsey: "", 0, undefined variables

{ print "expression" > "filename" }
{ print "expression" | "command" }
function add_tree (number) { # local variables can be declared here too, like &aux
    return number + 3
}
{ print add_tree(36) }

• Unique at the time due
  • being a scripting language
  • having associative arrays

• can assign a value on a if

  if (disjoint = r[2] <= m1 || m2 <= r[1])
      continue
  

• wEiRd - removes leading space

  $ awk '{ $1=$1 }1' file.txt
  $ awk '{ $1=$1 }; { print }' file.txt
  $ awk '/.*/ { $1=$1 }; /.*/ { print $0 }' file.txt
  

• array

  function format_matrix(    arr, row, col, res) {
      for (row in arr) {
          for (col in arr[row]) res = res sprintf(arr[row][col])
          res = res sprintf("\n")
      }
      return res
  }
  function print_matrix_dimensions(    arr) {
      printf "%dx%d\n", length(arr), length(arr[1])
  }
  

• math

  function max(    x,y) { return (x>y)?x:y  }
  function min(    x,y) { return (x<y)?x:y  }
  function abs(    x)   { return (x<0)?-x:x }
  

• untestes stack?

  function isEmpty()    { return idx == 0 }
  function peek()       { return stack[idx] }
  function push(el)     { print el; stack[++idx] = el }
  function pop(    tmp) { tmp = stack[idx]; delete stack[idx--]; return tmp }
  

• tested stack?

  function push(a, x) {
      "" in a # coerce into array
      a[length(a) + 1] = x
  }
  
  function pop(a, __x, __i) {
      __x = a[1]
      for (__i = 1; __i < length(a); __i++) a[__i] = a[__i + 1]
      delete a[__i]
      return __x
  }
  

• PGM - grayscale 1-D array of a 2-D matrix

  function array2PGM(arr,    out) {
      out = out "P2"    # format id
      out = out NF" "NR # dimensions
      out = out 9       # max value
      for (idx in cache)
          out = out arr[idx] " "
      return out "\n"
  }
  

$ readelf -d /usr/bin/gawk | grep Shared # 689K
 0x0000000000000001 (NEEDED)             Shared library: [libsigsegv.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libreadline.so.8]
 0x0000000000000001 (NEEDED)             Shared library: [libmpfr.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgmp.so.10]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

$ readelf -d /usr/bin/mawk | grep Shared # 155K
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

• buffering
  • gawk unbuffered by default
  • mawk buffers by default, needs -W interactive to disable

• editor tools
  • https://github.com/Beaglefoot/awk-language-server
  • https://emacs-lsp.github.io/lsp-mode/page/lsp-awk/
• coverage
  • https://benhoyt.com/writings/goawk-coverage/