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This task is quite easy while using the {{{printf}}} builtin. You can either write two simple functions as shown below or use the plain {{{printf}}} constructions alone. |
If you have a known octal or hexadecimal value (at script-writing time), you can just use `printf`: |
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| # 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. 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: {{{ # POSIX |
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| hex() { | # hex() - converts ASCII character to a hexadecimal value # unhex() - converts a hexadecimal value to an ASCII character hex() { |
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| unhex() { printf \\x"$1" } |
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| The {{{ord}}} function above is quite tricky. | |
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| The {{{ord}}} function above is quite tricky. It can be re-written in several other ways (use that one that will best suite your coding style or your actual needs). | . ''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 [[http://www.opengroup.org/onlinepubs/009695399/utilities/printf.html|printf()]] to know more) -- mjf'' |
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| ''Q: 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'' ''A: 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 [http://www.opengroup.org/onlinepubs/009695399/utilities/printf.html printf()] to know more) -- mjf'' |
This version of {{{chr}}} executes much faster than the {{{printf}}} version above (about 1/40 to less than 1/150 the time when run in a loop): |
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| ord() { printf '%d' \"$1\" } |
chr() { echo -en "\0$(( $1 % 8 + 10 * ( $1 / 8 ) + 20 ))"; } |
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| {{{ for p in chr newchr; do time for i in {1..4000}; do $p 65 >/dev/null; done; done |
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| Or: | System1 System2 real 0m46.824s real 1m33.814s user 0m4.624s user 0m8.540s sys 0m33.290s sys 1m23.978s |
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| {{{ ord() { printf '%d' \'$1\' } |
real 0m1.340s real 0m0.512s user 0m1.096s user 0m0.389s sys 0m0.124s sys 0m0.096s |
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| This version is faster as it executes without a subshell, it seems to only work strictly on ascii chars <127 while the printf version is happy with chars up to 255 and also for only a subset of ascii ie >64 decimal. | |
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| Or, rather: | |
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| {{{ ord() { printf '%d' "'$1'" } }}} |
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| Etc. All of the above {{{ord}}} functions should work properly. Which one you choose highly depends on particular situation. |
How do I convert an ASCII character to its decimal (or hexadecimal) value and back?
If you have a known octal or hexadecimal value (at script-writing time), you can just use printf:
# POSIX printf '\x27\047\n'
This prints two literal ' characters (27 is the hexadecimal ASCII value of the character, and 47 is the octal value) and a newline.
If you need to convert characters (or numeric ASCII values) that are not known in advance (i.e., in variables), you can use something a little more complicated:
# POSIX
# chr() - converts decimal value to its ASCII character representation
# ord() - converts ASCII character to its decimal value
chr() {
printf \\$(printf '%03o' $1)
}
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 $(chr 65) # -> 65The ord function above is quite tricky.
Tricky? Rather, it's using a feature that I can't find documented anywhere -- putting a single quote in front of an integer. Neat effect, but how on earth did you find out about it? Source diving? -- GreyCat
It validates The Single Unix Specification: "If the leading character is a single-quote or double-quote, the value shall be the numeric value in the underlying codeset of the character following the single-quote or double-quote." (see printf() to know more) -- mjf
This version of chr executes much faster than the printf version above (about 1/40 to less than 1/150 the time when run in a loop):
chr() { echo -en "\0$(( $1 % 8 + 10 * ( $1 / 8 ) + 20 ))"; } for p in chr newchr; do time for i in {1..4000}; do $p 65 >/dev/null; done; done
System1 System2
real 0m46.824s real 1m33.814s
user 0m4.624s user 0m8.540s
sys 0m33.290s sys 1m23.978s
real 0m1.340s real 0m0.512s
user 0m1.096s user 0m0.389s
sys 0m0.124s sys 0m0.096sThis version is faster as it executes without a subshell, it seems to only work strictly on ascii chars <127 while the printf version is happy with chars up to 255 and also for only a subset of ascii ie >64 decimal.