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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+$1%8)) } |
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This version of {{{chr}}} executes much faster than the {{{printf}}} version above (about 1/40 to less than 1/150 the time when run in a loop): {{{ chr() { echo -en "\0$(( $1 % 8 + 10 * ( $1 / 8 ) + 20 ))"; } }}} {{{ for p in chr newchr; do time for i in {1..4000}; do $p 65 >/dev/null; done; done System1 System2 real 0m46.824s real 1m33.814s user 0m4.624s user 0m8.540s sys 0m33.290s sys 1m23.978s real 0m1.340s real 0m0.512s user 0m1.096s user 0m0.389s sys 0m0.124s sys 0m0.096s }}} This version is faster as it executes without a subshell, it seems to only work strictly on ascii chars <127 while the printf version is happy with chars up to 255 and also for only a subset of ascii ie >64 decimal. |
How do I convert an ASCII character to its decimal (or hexadecimal) value and back?
If you have a known octal or hexadecimal value (at script-writing time), you can just use printf:
# POSIX printf '\x27\047\n'
This prints two literal ' characters (27 is the hexadecimal ASCII value of the character, and 47 is the octal value) and a newline.
If you need to convert characters (or numeric ASCII values) that are not known in advance (i.e., in variables), you can use something a little more complicated:
# POSIX
# chr() - converts decimal value to its ASCII character representation
# ord() - converts ASCII character to its decimal value
chr() {
printf \\$(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) # -> 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