Question

我有一个带有2个参数的bash脚本 - 一个字符和一个整数。我想在aplhabet中打印字符，从该整数的长度字符开始（以字母为模）

#!/bin/bash

[[ $# != 2 ]] && echo Exactly 2 argument needed && exit 1
[[ "$1" =~ ^[a-zA-Z]$ ]] || { echo Enter only one char; exit 2; }
[[ "$2" =~ ^[0-9]+$ ]] || { echo Enter integer; exit 3; }

letter="$1"
cnt="$2"
letter=`printf "%d" \'$letter`;
z=`printf "%d" \'z`
a=`printf "%d" \'a`
[[ "$1" =~ ^[[:upper:]]$ ]] && { ((letter+=32)); }           # make lower

while [[ "$cnt" -gt 0 ]]; do

  printf \\$(printf "%03o" "$letter")
  ((letter++))
  [[ "$letter" -gt $z  ]] && letter=$a                       # alphabet modulo
  ((cnt--))
done   
echo ""

这个脚本运行得很好，但速度太慢了。我必须调用printf程序的2x n（int值）。

我的问题是，是否有类似enable printf工作解决方案来提高printf执行速度或某些解决方案根本不使用printf。

我需要使用bash，我只想知道如何以最快的方式处理ASCII。我正在使用cygwin atm编写脚本，因此可能存在与之相关的速度失败。

这个脚本只是问题的一个例子，我不想要一些“增加stdout flush buffer size”的解决方案。谢谢:)）

Answer 1

你走了：

#!/bin/bash

[[ $# != 2 ]] && echo Exactly 2 argument needed && exit 1
[[ "$1" =~ ^[a-zA-Z]$ ]] || { echo Enter only one char; exit 2; }
[[ "$2" =~ ^[0-9]+$ ]] || { echo Enter integer; exit 3; }

alpha=`echo {a..z}|sed 's/ //g'`
letter="$1"
cnt="$2"
letter=$(expr `printf "%d - %d + 1" \'$letter \'a`;)

[[ "$1" =~ ^[[:upper:]]$ ]] && { ((letter+=32)); }           # make lower

echo -n `echo $alpha |tail -c +$letter |head -c $cnt`
((cnt=cnt-26))
while [[ "$cnt" -gt 0 ]]; do
    echo -n `echo $alpha |head -c $cnt`
    ((cnt=cnt-26))
done
echo ""

此程序使用大括号扩展将a..z扩展到字符列表中，然后使用头部和尾部显示此字符串的大小。它甚至可以更加优化，但这对你来说是一种练习。

效果比较（<1>是有问题的代码，<2>是此答案中的代码）：
*启动部分在<2>中有4个命令，而<1>中有3个命令 * <2>每26个字符运行4个命令（echo（x2），head，tail），而<1>中每个字符1个命令。 * <2>每26个字符有一个算术运算，而<1>每个字符有2个算术运算。

samveen@precise:/tmp$ time bash 1.sh a 1000
abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkl

real    0m2.065s
user    0m0.244s
sys     0m0.552s
samveen@precise:/tmp$ time bash 2.sh a 1000
abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkl

real    0m0.285s
user    0m0.024s
sys     0m0.060s

进一步阅读：man bash

Bash - 使用ASCII这么慢

1 个答案: