AWK

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

• gawk version changelog (by date)
  • 2023 (5.3)
    • --csv flag, supports fields surrounded by double quotes
    • \u escape sequence

• print unique lines, without sorting

  $ awk '!x[$0]++' file.txt
  

• 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
  }
  # map[i+((NR-1)*NF)] = $i
  function print_mat(    rid, cid) {
      print ""
      for (rid = 1; rid <= NR; rid++) {
          for (cid = 1; cid <= NF; cid++) {
              printf map[cid + ((rid-1)*NR)]
          }
          printf "\n"
      }
  }
  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"
  }
  

• check for empty records and fields

  length($0) == 0 { print "this is an empty record==" }
  END { if (NR == 0) print "means that we didn't process any record" }
  

$ 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