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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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#Another version doing the octal conversion with arithmetic # faster as it avoids a subshell chr () { printf \\$(($1/64*100+$1%64/8*10+$1%8)) } |
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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). ''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'' {{{ ord() { printf '%d' \"$1\" } }}} Or: {{{ ord() { printf '%d' \'$1\' } }}} Or, rather: {{{ ord() { printf '%d' "'$1'" } }}} Etc. All of the above {{{ord}}} functions should work properly. Which one you choose highly depends on particular situation. |
. ''Tricky? Rather, it's using a feature that I can't find documented anywhere -- putting a single quote in front of an integer. Neat effect, but how on '''earth''' did you find out about it? Source diving? -- GreyCat'' . ''It validates The Single Unix Specification: "If the leading character is a single-quote or double-quote, the value shall be the numeric value in the underlying codeset of the character following the single-quote or double-quote." (see [[http://www.opengroup.org/onlinepubs/009695399/utilities/printf.html|printf()]] to know more) -- mjf'' |
How do I convert an ASCII character to its decimal (or hexadecimal) value and back?
If you have a known octal or hexadecimal value (at script-writing time), you can just use printf:
# POSIX printf '\x27\047\n'
This prints two literal ' characters (27 is the hexadecimal ASCII value of the character, and 47 is the octal value) and a newline.
If you need to convert characters (or numeric ASCII values) that are not known in advance (i.e., in variables), you can use something a little more complicated:
# POSIX # chr() - converts decimal value to its ASCII character representation # ord() - converts ASCII character to its decimal value chr() { printf \\$(printf '%03o' $1) } #Another version doing the octal conversion with arithmetic # faster as it avoids a subshell chr () { printf \\$(($1/64*100+$1%64/8*10+$1%8)) } 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