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先看C语言的一段代码
#include <stdio.h>
int main(int argc, char* argv[]) { int i, sum; i = 0; sum = 0; loop: i++; sum += i; if (i <= 100) { goto loop; } printf("sum = %d\n", sum); return 0; }
这样看起来是不是有点困难。
如果整理一下格式：
#include <stdio.h>
int main(int argc, char* argv[])
{
int i, sum;
i = 0;
sum = 0;
loop:
i++;
sum += i;
if (i <= 100)
{
goto loop;
}
printf("sum = %d\n", sum);
return 0;
}
理解起来很容易。
sed 标签示例：
sed -e ":begin; { />>>/! { $! { N; b begin }; }; s/<<<.*>>>/COMMENT/; };" test
sed的标签也很容易，仅仅因为sed的语句习惯写在一行，所以形式上看起来比较复杂。
 xx 定义标签，注意和C语言的不同，C语言是 xxx:，sed中冒号在lable前面， C语言中冒号在lable后面。
:a ba 强制跳转 ： 无条件goto
:a ta 成功跳转 ： 有条件goto
man:
b label
Branch to label; if label is omitted, branch to end of script.
t label
If a s/// has done a successful substitution since the last input line was read and since the
last t or T command, then branch to label; if label is omitted, branch to end of script.
T label
If no s/// has done a successful substitution since the last input line was read and since the
last t or T command, then branch to label; if label is omitted, branch to end of script. |
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发表于 2010-01-26 09:03
发表于 2010-01-26 09:48
