Diff for "BashFAQ/071"

How do I convert an ASCII character to its decimal (or hexadecimal) value and back?

If you have a known octal or hexadecimal value (at script-writing time), you can just use printf:

   # POSIX
   printf '\x27\047\n'

This prints two literal ' characters (27 is the hexadecimal ASCII value of the character, and 47 is the octal value) and a newline.

   ExpandedString=$'\x27\047\u0027\U00000027\n'
   echo -n "$ExpandedString"

Another approach $'...' strings are escaped before evaluation and can be embedded directly in code.

If you need to convert characters (or numeric ASCII values) that are not known in advance (i.e., in variables), you can use something a little more complicated:

• The following example was submitted quite recently and needs to be cleaned up and validated. In particular, the function names with periods in them are abusing an undocumented, possibly unintended bash parsing glitch.

  ###############################################################
  #
  #       Note about Ext Ascii and UTF-8 encoding
  #
  # for values 0x00   - 0x7f        Identical
  # for values 0x80   - 0xff        conflict between UTF-8 & ExtAscii
  # for values 0x100  - 0xffff      Only UTF-8 UTF-16 UTF-32
  # for values 0x100  - 0x7FFFFFFF  Only UTF-8 UTF-32
  #
  # value         EAscii   UTF-8                          UTF-16  UTF-32
  # 0x20          "\x20"  "\x20"                          \u0020  \U00000020
  # 0x20          "\x7f"  "\x7f"                          \u007f  \U0000007f
  # 0x80          "\x80"  "\xc2\x80"                      \u0080  \U00000080
  # 0xff          "\xff"  "\xc3\xbf"                      \u00ff  \U000000ff
  # 0x100         N/A     "\xc4\x80"                      \u0100  \U00000100
  # 0x1000        N/A     "\xc8\x80"                      \u1000  \U00001000
  # 0xffff        N/A     "\xef\xbf\xbf"                  \uffff  \U0000ffff
  # 0x10000       N/A     "\xf0\x90\x80\x80"              N/A     \U00010000
  # 0xfffff       N/A     "\xf3\xbf\xbf\xbf"              N/A     \U000fffff
  # 0x10000000    N/A     "\xfc\x90\x80\x80\x80\x80"      N/A     \U10000000
  # 0x7fffffff    N/A     "\xfd\xbf\xbf\xbf\xbf\xbf"      N/A     \U7fffffff
  # 0x80000000    N/A     N/A                             N/A     N/A
  # 0xffffffff    N/A     N/A                             N/A     N/A

  ###########################################################################
  ## ord family
  ###########################################################################
  # ord        <Return Variable Name> <Char to convert> [Optional Format String]
  # ord_hex    <Return Variable Name> <Char to convert>
  # ord_oct    <Return Variable Name> <Char to convert>
  # ord_utf8   <Return Variable Name> <Char to convert> [Optional Format String]
  # ord_eascii <Return Variable Name> <Char to convert> [Optional Format String]
  # ord_echo                      <Char to convert> [Optional Format String]
  # ord_hex_echo                  <Char to convert>
  # ord_oct_echo                  <Char to convert>
  # ord_utf8_echo                 <Char to convert> [Optional Format String]
  # ord_eascii_echo               <Char to convert> [Optional Format String]
  #
  # Description:
  # converts character using native encoding to its decimal value and stores
  # it in the Variable specified
  #
  #       ord
  #       ord_hex         output in hex
  #       ord_hex         output in octal
  #       ord_utf8        forces UTF8 decoding
  #       ord_eascii      forces eascii decoding
  #       ord_echo        prints to stdout
  function ord {
          printf -v "${1?Missing Dest Variable}" "${3:-%d}" "'${2?Missing Char}"
  }
  function ord_oct {
          ord "${@:1:2}" "0%c"
  }
  function ord_hex {
          ord "${@:1:2}" "0x%x"
  }
  function ord_utf8 {
          LC_CTYPE=C.UTF-8 ord "${@}"
  }
  function ord_eascii {
          LC_CTYPE=C ord "${@}"
  }
  function ord_echo {
          printf "${2:-%d}" "'${1?Missing Char}"
  }
  function ord_oct_echo {
          ord_echo "${1}" "0%o"
  }
  function ord_hex_echo {
          ord_echo "${1}" "0x%x"
  }
  function ord_utf8_echo {
          LC_CTYPE=C.UTF-8 ord_echo "${@}"
  }
  function ord_eascii_echo {
          LC_CTYPE=C ord_echo "${@}"
  }

  ###########################################################################
  ## chr family
  ###########################################################################
  # chr_utf8   <Return Variale Name> <Integer to convert>
  # chr_eascii <Return Variale Name> <Integer to convert>
  # chr        <Return Variale Name> <Integer to convert>
  # chr_oct    <Return Variale Name> <Octal number to convert>
  # chr_hex    <Return Variale Name> <Hex number to convert>
  # chr_utf8_echo                  <Integer to convert>
  # chr_eascii_echo                <Integer to convert>
  # chr_echo                       <Integer to convert>
  # chr_oct_echo                   <Octal number to convert>
  # chr_hex_echo                   <Hex number to convert>
  #
  # Description:
  # converts decimal value to character representation an stores
  # it in the Variable specified
  #
  #       chr                     Tries to guess output format
  #       chr_utf8                forces UTF8 encoding
  #       chr_eascii              forces eascii encoding
  #       chr_echo                prints to stdout
  #
  function chr_utf8 {
          local val
          [[ ${2?Missing Ordinal Value} -lt 0x80000000 ]] || return 1

          if [[ ${2} -lt 0x100 && ${2} -ge 0x80 ]]; then
                  # some kinda weird bash? behavior
                  # treats \Uff as \xff so encode manually
                  printf -v val "\\%03o\%03o" $(( (${2}>>6)|0xc0 )) $(( (${2}&0x3f)|0x80 ))
          else
                  printf -v val '\\U%08x' "${2}"
          fi
          printf -v ${1?Missing Dest Variable} ${val}
  }
  function chr_eascii {
          local val
          # Make sure value less than 0x100
          # otherwise we end up with
          # \xVVNNNNN
          # where \xVV = char && NNNNN is a number string
          # so chr "0x44321" => "D321"
          [[ ${2?Missing Ordinal Value} -lt 0x100 ]] || return 1
          printf -v val '\\x%02x' "${2}"
          printf -v ${1?Missing Dest Variable} ${val}
  }
  function chr {
          if [ "${LC_CTYPE:-${LC_ALL:-}}" = "C" ]; then
                  chr_eascii "${@}"
          else
                  chr_utf8 "${@}"
          fi
  }
  function chr_dec {
          # strip leading 0s otherwise
          # interpreted as Octal
          if shopt extglob &>/dev/null ;then
                  chr "${1}" "${2/#+(0)}"
          else
                  shopt -s extglob
                  chr "${1}" "${2/#+(0)}"
                  shopt -u extglob
          fi
  }
  function chr_oct {
          chr "${1}" "0${2}"
  }
  function chr_hex {
          chr "${1}" "0x${2}"
  }
  function chr_utf8_echo {
          local val
          [[ ${1?Missing Ordinal Value} -lt 0x80000000 ]] || return 1

          if [[ ${1} -lt 0x100 && ${1} -ge 0x80 ]]; then
                  # some kinda weird bash? behavior
                  # treats \Uff as \xff so encode manually
                  printf -v val '\\%03o\\%03o' $(( (${1}>>6)|0xc0 )) $(( (${1}&0x3f)|0x80 ))
          else
                  printf -v val '\\U%08x' "${1}"
          fi
          printf "${val}"
  }
  function chr_eascii_echo {
          local val
          # Make sure value less than 0x100
          # otherwise we end up with
          # \xVVNNNNN
          # where \xVV = char && NNNNN is a number string
          # so chr "0x44321" => "D321"
          [[ ${1?Missing Ordinal Value} -lt 0x100 ]] || return 1
          printf -v val '\\x%x' "${1}"
          printf "${val}"
  }
  function chr_echo {
          if [ "${LC_CTYPE:-${LC_ALL:-}}" = "C" ]; then
                  chr_eascii_echo "${@}"
          else
                  chr_utf8_echo "${@}"
          fi
  }
  function chr_dec_echo {
          # strip leading 0s otherwise
          # interpreted as Octal
          if shopt extglob &>/dev/null ;then
                  chr_echo "${1/#+(0)}"
          else
                  shopt -s extglob
                  chr_echo "${1/#+(0)}"
                  shopt -u extglob
          fi
  }
  function chr_oct_echo {
          chr_echo "0${1}"
  }
  function chr_hex_echo {
          chr_echo "0x${1}"
  }

  #
  # Simple Validation code
  #
  function test_echo_func {
    local Outcome _result
    _result="$( "${1}" "${2}" )"
    [ "${_result}" = "${3}" ] && Outcome="Pass" || Outcome="Fail"
    printf "# %-20s %-6s => "           "${1}" "${2}" "${_result}" "${3}"
    printf "[ "%16q" = "%-16q"%-5s ] "  "${_result}" "${3}" "(${3//[[:cntrl:]]/_})"
    printf "%s\n"                       "${Outcome}"


  }
  function test_value_func {
    local Outcome _result
    "${1}" _result "${2}"
    [ "${_result}" = "${3}" ] && Outcome="Pass" || Outcome="Fail"
    printf "# %-20s %-6s => "           "${1}" "${2}" "${_result}" "${3}"
    printf "[ "%16q" = "%-16q"%-5s ] "  "${_result}" "${3}" "(${3//[[:cntrl:]]/_})"
    printf "%s\n"                       "${Outcome}"
  }
  test_echo_func  chr_echo "$(ord_echo  "A")"  "A"
  test_echo_func  ord_echo "$(chr_echo "65")"  "65"
  test_echo_func  chr_echo "$(ord_echo  "ö")"  "ö"
  test_value_func chr      "$(ord_echo  "A")"  "A"
  test_value_func ord      "$(chr_echo "65")"  "65"
  test_value_func chr      "$(ord_echo  "ö")"  "ö"
  # chr_echo             65     => [                A = A               (A)   ] Pass
  # ord_echo             A      => [               65 = 65              (65)  ] Pass
  # chr_echo             246    => [      $'\303\266' = $'\303\266'     (ö)  ] Pass
  # chr                  65     => [                A = A               (A)   ] Pass
  # ord                  A      => [               65 = 65              (65)  ] Pass
  # chr                  246    => [      $'\303\266' = $'\303\266'     (ö)  ] Pass
  #


  test_echo_func  chr_echo     "65"     A
  test_echo_func  chr_echo     "065"    5
  test_echo_func  chr_dec_echo "065"    A
  test_echo_func  chr_oct_echo "65"     5
  test_echo_func  chr_hex_echo "65"     e
  test_value_func chr          "65"     A
  test_value_func chr          "065"    5
  test_value_func chr_dec      "065"    A
  test_value_func chr_oct      "65"     5
  test_value_func chr_hex      "65"     e
  # chr_echo             65     => [                A = A               (A)   ] Pass
  # chr_echo             065    => [                5 = 5               (5)   ] Pass
  # chr_dec_echo         065    => [                A = A               (A)   ] Pass
  # chr_oct_echo         65     => [                5 = 5               (5)   ] Pass
  # chr_hex_echo         65     => [                e = e               (e)   ] Pass
  # chr                  65     => [                A = A               (A)   ] Pass
  # chr                  065    => [                5 = 5               (5)   ] Pass
  # chr_dec              065    => [                A = A               (A)   ] Pass
  # chr_oct              65     => [                5 = 5               (5)   ] Pass
  # chr_hex              65     => [                e = e               (e)   ] Pass

  #test_value_func chr          0xff   $'\xff'
  test_value_func chr_eascii   0xff   $'\xff'
  test_value_func chr_utf8     0xff   $'\uff'      # Note this fails because bash encodes it incorrectly
  test_value_func chr_utf8     0xff   $'\303\277'
  test_value_func chr_utf8     0x100  $'\u100'
  test_value_func chr_utf8     0x1000 $'\u1000'
  test_value_func chr_utf8     0xffff $'\uffff'
  # chr_eascii           0xff   => [          $'\377' = $'\377'         (�)   ] Pass
  # chr_utf8             0xff   => [      $'\303\277' = $'\377'         (�)   ] Fail
  # chr_utf8             0xff   => [      $'\303\277' = $'\303\277'     (ÿ)  ] Pass
  # chr_utf8             0x100  => [      $'\304\200' = $'\304\200'     (Ā)  ] Pass
  # chr_utf8             0x1000 => [  $'\341\200\200' = $'\341\200\200' (က) ] Pass
  # chr_utf8             0xffff => [  $'\357\277\277' = $'\357\277\277' (���) ] Pass
  test_value_func ord_utf8     "A"           65
  test_value_func ord_utf8     "ä"          228
  test_value_func ord_utf8     $'\303\277'  255
  test_value_func ord_utf8     $'\u100'     256



  #########################################################
  # to help debug problems try this
  #########################################################
  printf "%q\n" $'\xff'                  # => $'\377'
  printf "%q\n" $'\uffff'                # => $'\357\277\277'
  printf "%q\n" "$(chr_utf8_echo 0x100)" # => $'\304\200'
  #
  # This can help a lot when it comes to diagnosing problems
  # with read and or xterm program output
  # I use it a lot in error case to create a human readable error message
  # i.e.
  echo "Enter type to test, Enter to continue"
  while read -srN1 ; do
    ord asciiValue "${REPLY}"
    case "${asciiValue}" in
      10) echo "Goodbye" ; break ;;
      20|21|22) echo "Yay expected input" ;;
      *) printf ':( Unexpected Input 0x%02x %q "%s"\n' "${asciiValue}" "${REPLY}" "${REPLY//[[:cntrl:]]}" ;;
    esac
  done

  #########################################################
  # More exotic approach 1
  #########################################################
  # I used to use this before I figured out the LC_CTYPE=C approach
  # printf "EAsciiLookup=%q" "$(for (( x=0x0; x<0x100 ; x++)); do printf '%b' $(printf '\\x%02x' "$x"); done)"
  EAsciiLookup=$'\001\002\003\004\005\006\a\b\t\n\v\f\r\016\017\020\021\022\023'
  EAsciiLookup+=$'\024\025\026\027\030\031\032\E\034\035\036\037 !"#$%&\'()*+,-'
  EAsciiLookup+=$'./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghi'
  EAsciiLookup+=$'jklmnopqrstuvwxyz{|}~\177\200\201\202\203\204\205\206\207\210'
  EAsciiLookup+=$'\211\212\213\214\215\216\217\220\221\222\223\224\225\226\227'
  EAsciiLookup+=$'\230\231\232\233\234\235\236\237\240\241\242\243\244\245\246'
  EAsciiLookup+=$'\247\250\251\252\253\254\255\256\257\260\261\262\263\264\265'
  EAsciiLookup+=$'\266\267\270\271\272\273\274\275\276\277\300\301\302\303\304'
  EAsciiLookup+=$'\305\306\307\310\311\312\313\314\315\316\317\320\321\322\323'
  EAsciiLookup+=$'\324\325\326\327\330\331\332\333\334\335\336\337\340\341\342'
  EAsciiLookup+=$'\343\344\345\346\347\350\351\352\353\354\355\356\357\360\361'
  EAsciiLookup+=$'\362\363\364\365\366\367\370\371\372\373\374\375\376\377'
  function ord_eascii2 {
    local idx="${EAsciiLookup%%${2:0:1}*}"
    eval ${1}'=$(( ${#idx} +1 ))'
  }

  #########################################################
  # More exotic approach 2
  #########################################################
  #printf "EAsciiLookup2=(\n    %s\n)" "$(for (( x=0x1; x<0x100 ; x++)); do printf '%-18s'  "$(printf '[_%q]="0x%02x"' "$(printf "%b" "$(printf '\\x%02x' "$x")")" $x )" ; [ "$(($x%6))" != "0" ] || echo -en "\n    " ; done)"
  typeset -A EAsciiLookup2
  EAsciiLookup2=(
    [_$'\001']="0x01" [_$'\002']="0x02" [_$'\003']="0x03" [_$'\004']="0x04"
    [_$'\005']="0x05" [_$'\006']="0x06" [_$'\a']="0x07"   [_$'\b']="0x08"
    [_$'\t']="0x09"   [_'']="0x0a"      [_$'\v']="0x0b"   [_$'\f']="0x0c"
    [_$'\r']="0x0d"   [_$'\016']="0x0e" [_$'\017']="0x0f" [_$'\020']="0x10"
    [_$'\021']="0x11" [_$'\022']="0x12" [_$'\023']="0x13" [_$'\024']="0x14"
    [_$'\025']="0x15" [_$'\026']="0x16" [_$'\027']="0x17" [_$'\030']="0x18"
    [_$'\031']="0x19" [_$'\032']="0x1a" [_$'\E']="0x1b"   [_$'\034']="0x1c"
    [_$'\035']="0x1d" [_$'\036']="0x1e" [_$'\037']="0x1f" [_\ ]="0x20"
    [_\!]="0x21"      [_\"]="0x22"      [_\#]="0x23"      [_\$]="0x24"
    [_%]="0x25"       [_\&]="0x26"      [_\']="0x27"      [_\(]="0x28"
    [_\)]="0x29"      [_\*]="0x2a"      [_+]="0x2b"       [_\,]="0x2c"
    [_-]="0x2d"       [_.]="0x2e"       [_/]="0x2f"       [_0]="0x30"
    [_1]="0x31"       [_2]="0x32"       [_3]="0x33"       [_4]="0x34"
    [_5]="0x35"       [_6]="0x36"       [_7]="0x37"       [_8]="0x38"
    [_9]="0x39"       [_:]="0x3a"       [_\;]="0x3b"      [_\<]="0x3c"
    [_=]="0x3d"       [_\>]="0x3e"      [_\?]="0x3f"      [_@]="0x40"
    [_A]="0x41"       [_B]="0x42"       [_C]="0x43"       [_D]="0x44"
    [_E]="0x45"       [_F]="0x46"       [_G]="0x47"       [_H]="0x48"
    [_I]="0x49"       [_J]="0x4a"       [_K]="0x4b"       [_L]="0x4c"
    [_M]="0x4d"       [_N]="0x4e"       [_O]="0x4f"       [_P]="0x50"
    [_Q]="0x51"       [_R]="0x52"       [_S]="0x53"       [_T]="0x54"
    [_U]="0x55"       [_V]="0x56"       [_W]="0x57"       [_X]="0x58"
    [_Y]="0x59"       [_Z]="0x5a"       [_\[]="0x5b"      #[_\\]="0x5c"
    #[_\]]="0x5d"
                      [_\^]="0x5e"      [__]="0x5f"       [_\`]="0x60"
    [_a]="0x61"       [_b]="0x62"       [_c]="0x63"       [_d]="0x64"
    [_e]="0x65"       [_f]="0x66"       [_g]="0x67"       [_h]="0x68"
    [_i]="0x69"       [_j]="0x6a"       [_k]="0x6b"       [_l]="0x6c"
    [_m]="0x6d"       [_n]="0x6e"       [_o]="0x6f"       [_p]="0x70"
    [_q]="0x71"       [_r]="0x72"       [_s]="0x73"       [_t]="0x74"
    [_u]="0x75"       [_v]="0x76"       [_w]="0x77"       [_x]="0x78"
    [_y]="0x79"       [_z]="0x7a"       [_\{]="0x7b"      [_\|]="0x7c"
    [_\}]="0x7d"      [_~]="0x7e"       [_$'\177']="0x7f" [_$'\200']="0x80"
    [_$'\201']="0x81" [_$'\202']="0x82" [_$'\203']="0x83" [_$'\204']="0x84"
    [_$'\205']="0x85" [_$'\206']="0x86" [_$'\207']="0x87" [_$'\210']="0x88"
    [_$'\211']="0x89" [_$'\212']="0x8a" [_$'\213']="0x8b" [_$'\214']="0x8c"
    [_$'\215']="0x8d" [_$'\216']="0x8e" [_$'\217']="0x8f" [_$'\220']="0x90"
    [_$'\221']="0x91" [_$'\222']="0x92" [_$'\223']="0x93" [_$'\224']="0x94"
    [_$'\225']="0x95" [_$'\226']="0x96" [_$'\227']="0x97" [_$'\230']="0x98"
    [_$'\231']="0x99" [_$'\232']="0x9a" [_$'\233']="0x9b" [_$'\234']="0x9c"
    [_$'\235']="0x9d" [_$'\236']="0x9e" [_$'\237']="0x9f" [_$'\240']="0xa0"
    [_$'\241']="0xa1" [_$'\242']="0xa2" [_$'\243']="0xa3" [_$'\244']="0xa4"
    [_$'\245']="0xa5" [_$'\246']="0xa6" [_$'\247']="0xa7" [_$'\250']="0xa8"
    [_$'\251']="0xa9" [_$'\252']="0xaa" [_$'\253']="0xab" [_$'\254']="0xac"
    [_$'\255']="0xad" [_$'\256']="0xae" [_$'\257']="0xaf" [_$'\260']="0xb0"
    [_$'\261']="0xb1" [_$'\262']="0xb2" [_$'\263']="0xb3" [_$'\264']="0xb4"
    [_$'\265']="0xb5" [_$'\266']="0xb6" [_$'\267']="0xb7" [_$'\270']="0xb8"
    [_$'\271']="0xb9" [_$'\272']="0xba" [_$'\273']="0xbb" [_$'\274']="0xbc"
    [_$'\275']="0xbd" [_$'\276']="0xbe" [_$'\277']="0xbf" [_$'\300']="0xc0"
    [_$'\301']="0xc1" [_$'\302']="0xc2" [_$'\303']="0xc3" [_$'\304']="0xc4"
    [_$'\305']="0xc5" [_$'\306']="0xc6" [_$'\307']="0xc7" [_$'\310']="0xc8"
    [_$'\311']="0xc9" [_$'\312']="0xca" [_$'\313']="0xcb" [_$'\314']="0xcc"
    [_$'\315']="0xcd" [_$'\316']="0xce" [_$'\317']="0xcf" [_$'\320']="0xd0"
    [_$'\321']="0xd1" [_$'\322']="0xd2" [_$'\323']="0xd3" [_$'\324']="0xd4"
    [_$'\325']="0xd5" [_$'\326']="0xd6" [_$'\327']="0xd7" [_$'\330']="0xd8"
    [_$'\331']="0xd9" [_$'\332']="0xda" [_$'\333']="0xdb" [_$'\334']="0xdc"
    [_$'\335']="0xdd" [_$'\336']="0xde" [_$'\337']="0xdf" [_$'\340']="0xe0"
    [_$'\341']="0xe1" [_$'\342']="0xe2" [_$'\343']="0xe3" [_$'\344']="0xe4"
    [_$'\345']="0xe5" [_$'\346']="0xe6" [_$'\347']="0xe7" [_$'\350']="0xe8"
    [_$'\351']="0xe9" [_$'\352']="0xea" [_$'\353']="0xeb" [_$'\354']="0xec"
    [_$'\355']="0xed" [_$'\356']="0xee" [_$'\357']="0xef" [_$'\360']="0xf0"
    [_$'\361']="0xf1" [_$'\362']="0xf2" [_$'\363']="0xf3" [_$'\364']="0xf4"
    [_$'\365']="0xf5" [_$'\366']="0xf6" [_$'\367']="0xf7" [_$'\370']="0xf8"
    [_$'\371']="0xf9" [_$'\372']="0xfa" [_$'\373']="0xfb" [_$'\374']="0xfc"
    [_$'\375']="0xfd" [_$'\376']="0xfe" [_$'\377']="0xff"
  )
  function ord_eascii3 {
        local -i val="${EAsciiLookup2["_${2:0:1}"]-}"
        if [ "${val}" -eq 0 ]; then
                case "${2:0:1}" in
                        ])  val=0x5d ;;
                        \\) val=0x5c ;;
                esac
        fi
        eval "${1}"'="${val}"'
  }
  # for fun check out the following
  time for (( i=0 ; i <1000; i++ )); do ord TmpVar 'a'; done
  #  real 0m0.065s
  #  user 0m0.048s
  #  sys  0m0.000s

  time for (( i=0 ; i <1000; i++ )); do ord_eascii TmpVar 'a'; done
  #  real 0m0.239s
  #  user 0m0.188s
  #  sys  0m0.000s

  time for (( i=0 ; i <1000; i++ )); do ord_utf8 TmpVar 'a'; done
  #  real       0m0.225s
  #  user       0m0.180s
  #  sys        0m0.000s

  time for (( i=0 ; i <1000; i++ )); do ord_eascii2 TmpVar 'a'; done
  #  real 0m1.507s
  #  user 0m1.056s
  #  sys  0m0.012s

  time for (( i=0 ; i <1000; i++ )); do ord_eascii3 TmpVar 'a'; done
  #  real 0m0.147s
  #  user 0m0.120s
  #  sys  0m0.000s

  time for (( i=0 ; i <1000; i++ )); do ord_echo 'a' >/dev/null ; done
  #  real       0m0.065s
  #  user       0m0.044s
  #  sys        0m0.016s

  time for (( i=0 ; i <1000; i++ )); do ord_eascii_echo 'a' >/dev/null ; done
  #  real       0m0.089s
  #  user       0m0.068s
  #  sys        0m0.008s

  time for (( i=0 ; i <1000; i++ )); do ord_utf8_echo 'a' >/dev/null ; done
  #  real       0m0.226s
  #  user       0m0.172s
  #  sys        0m0.012s

Here are some older, simpler functions that do similar things:

# POSIX
# chr() - converts decimal value to its ASCII character representation
# ord() - converts ASCII character to its decimal value

chr() {
  [ ${1} -lt 256 ] || return 1
  printf \\$(printf '%03o' $1)
}

# Another version doing the octal conversion with arithmetic
# faster as it avoids a subshell
chr () {
  [ ${1} -lt 256 ] || return 1
  printf \\$(($1/64*100+$1%64/8*10+$1%8))
}

# Another version using a temporary variable to avoid subshell.
# This one requires bash 3.1.
chr() {
  local tmp
  [ ${1} -lt 256 ] || return 1
  printf -v tmp '%03o' "$1"
  printf \\"$tmp"
}

ord() {
  printf '%d' "'$1"
}

# hex() - converts ASCII character to a hexadecimal value
# unhex() - converts a hexadecimal value to an ASCII character

hex() {
   printf '%x' "'$1"
}

unhex() {
   printf \\x"$1"
}

# examples:

chr $(ord A)    # -> A
ord $(chr 65)   # -> 65

The ord function above is quite tricky.

• Tricky? Rather, it's using a feature that I can't find documented anywhere -- putting a single quote in front of an integer. Neat effect, but how on earth did you find out about it? Source diving? -- GreyCat

  • It validates The Single Unix Specification: "If the leading character is a single-quote or double-quote, the value shall be the numeric value in the underlying codeset of the character following the single-quote or double-quote." (see printf() to know more) -- mjf

  $'\357\277\277'
  • printf "%q\n" "$(chr.utf8.echo 0x100)" # =