学步园

实现从文件中截取出从一个字符串开始到另一个字符串结束，之间所有的字符输出到另一个文件中。下面的批处理脚本实现从1_DDL.out文件中将所有在CREATE和分号之间的行输出到0.txt中。（一个CREATE对应紧随其后的分号为一组）

@echo off
Rem matching and extracting the create table statements
if exist 1_DDL.out (
  echo now extracting create table statements
  set myflag=false
  SetLocal EnableDelayedExpansion
  for /f "delims=" %%i in (1_DDL.out) do (
    echo %%i
    
    echo %%i|find "CREATE">nul && set myflag=true
    if "!myflag!" == "true" (
      echo %%i >> 0.txt
      rem echo %%i
    ) else (
      echo not matching...
    )
    echo %%i|find ";">nul && set myflag=false
  )
) else (
  echo not found 1_DDL.out
)
Rem deleting the unused file
echo clearing the unused files
del 1_DDL.out
echo Done.

上述批处理代码，存在一个问题：当输入文件1_DDL.out中含有大于号>等特殊符号时，匹配失败，且会有各种“奇怪”的现象。大家有兴趣可以自己试验一下。下面是经过增强的版本2：

Rem matching and extracting the create table statements
if exist 1_DDL.out (
  echo now extracting create table statements
  set myflag=false
  rem any good idea?
  set tempflag=false
  SetLocal EnableDelayedExpansion
  for /f "delims=" %%i in (1_DDL.out) do (
    echo %%i
    rem tackling the > operator
    
    rem echo "%%i"
    set tempflag = false
    echo %%i |find ";">nul && set tempflag=true
    echo "%%i"|find /i "create">nul && set myflag=true
    echo !myflag!
    if "!myflag!" == "true" (
      echo %%i >> DDL.txt
      rem echo %%i
    ) else (
      echo not matching...
    )
    rem the next sentence do nth if there is a > in current %%i
    rem echo %%i|find ";">nul && set myflag=false
    if "!tempflag!" == "true" set myflag=false
  )
  endlocal
) else (
  echo not found 1_DDL.out
)

上面的实现用了两个flag变量，逻辑有点绕。特别注意一下%%i加了引号。下面是逻辑较为清晰的代码：

Rem matching and extracting the create table statements
if exist 1_DDL.out (
  echo now extracting create table statements
  set myflag=false
  SetLocal EnableDelayedExpansion
  for /f "delims=" %%i in (1_DDL.out) do (
    echo %%i
    rem tackling the > operator
	
    echo "%%i"
    echo "%%i"|find /i "create">nul && set myflag=true
    echo myflag !myflag!
    if "!myflag!" == "true" (
      echo %%i >> DDL.txt
      rem echo %%i
    ) else (
      echo not matching...
    )
    echo "%%i"|find ";">nul && set myflag=false
  )
  endlocal
) else (
  echo not found 1_DDL.out
)

今天（2012年11月26号）发现之前写的这个bat，

echo "%%i"|find /i "create">nul && set myflag=true

这行执行时会报错find: `create': No such file or directory或者The process tried to write to a nonexistent pipe，很诧异，之前执行都未出现此问题，google了一段时间没有找到解决办法。最后只能先改成findstr了。哪位大虾有解决办法共享下。