How does this command create an empty file? - China DOS Union Forum

set d="echo a.txt > b.txt" & copy %d% > 1.txt & type 1.txt | find /i "echo" > b.txt

And here's another one, same effect as the one above
prompt echo$Sb.txt$S$Gc.txt& echo z|cmd|findstr /e "t">b.txt

This involves knowledge of setting variables in the DOS environment (the set command), and of pipe/redirection commands (> and |).
The one below involves knowledge of display commands under DOS (the echo command), the prompt command (prompt), the new DOS environment command (cmd, and this is the command command under win2000), and the string-search command (findstr, should be an external command, right?).
Please go look up the usage of these commands separately (including some special usages). After you understand them, then come back and think about this complicated composite command.

findstr ？？？？？？？？？？？ Shouldn't it be the find command? Format: find "string" /?

The following is quoted from dv's post on 2003-7-9 1:38:48:
findstr ？？？？？？？？？？？ Shouldn't it be the find command? Format: find "string" /?

Maybe. You might be right. I don't know what the OP is talking about either. I'm just guessing. Hehe...

The following is quoted from dv's post on 2003-7-9 1:38:48:
findstr ？？？？？？？？？？？ Shouldn't it be the find command? Format: find "string" /?

I don't think so......... findstr is a Win2000/XP command........

I remembered it wrong,,, there are find and findstr,,, and findstr is still more versatile,,, sorry for making a fool of myself

-----------Searches for strings in files using literal text or regular expressions. Click "Related Topics" in the list for "Devinfo Help" to get a list of the regular expression symbols accepted by findstr.

findstr filename ]

Parameters

/b

Matches the pattern if it is at the beginning of a line.

/e

Matches the pattern if it is at the end of a line.

/l

Uses a literal search string.

/c: string

Uses the specified text as a literal search string.

/r

Uses the search string as a regular expression. This switch is not needed, because unless the /l switch is used, findstr interprets all metacharacters as regular expressions.

/s

Searches for matching files in the current directory and all subdirectories.

/i

Specifies that the search is case-insensitive.

/x

Prints lines that match exactly.

/v

Prints only lines that do not contain a match.

/n

Prints the line number before each matching line.

/m

If the file contains a match, prints only the file name.

/o

Prints the character offset before each matching line.

/g filename

Gets search strings from the specified file.

/f file

Reads the file list from the specified file.

/d dirlist

Searches the comma-separated directory list.

set d="echo a.txt > b.txt"
At this point the contents of b.txt are a.txt

& copy %d% > 1.txt
copy %d% becomes 1.txt

& type 1.txt | find /i "echo" > b.txt
Search for the string echo in 1.txt; if found, write it into b.txt
if not, it will be empty

But note that what is used here is >
So no matter how many echo strings there are in 1.txt
the contents of b.txt will only be a single echo

And here's another one, same effect as the one above
prompt echo$Sb.txt$S$Gc.txt& echo z|cmd|findstr /e "t">b.txt

set d="echo a.txt>b.txt"
echo %d%>1.txt
type 1.txt | find /i "echo">b.txt

Why is there such a big difference between having an & and not having one? Doesn't & just serve as a connector? I feel this should have the same effect as the OP's version. But in reality the effect is very different

Floor1　lucifer	Posted 2003-06-30 00:00
初级用户　Posts 1　Credits 124
set d="echo a.txt > b.txt" & copy %d% > 1.txt & type 1.txt \| find /i "echo" > b.txt And here's another one, same effect as the one above prompt echo$Sb.txt$S$Gc.txt& echo z\|cmd\|findstr /e "t">b.txt

Floor2　ko20010214	Posted 2003-07-04 00:00
版主　Posts 1,628　Credits 7,296
This involves knowledge of setting variables in the DOS environment (the set command), and of pipe/redirection commands (> and \|). The one below involves knowledge of display commands under DOS (the echo command), the prompt command (prompt), the new DOS environment command (cmd, and this is the command command under win2000), and the string-search command (findstr, should be an external command, right?). Please go look up the usage of these commands separately (including some special usages). After you understand them, then come back and think about this complicated composite command.

Floor3　dv人	Posted 2003-07-09 00:00
初级用户　Posts 35　Credits 281
findstr ？？？？？？？？？？？ Shouldn't it be the find command? Format: find "string" /?

Floor4　ko20010214	Posted 2003-07-09 00:00
版主　Posts 1,628　Credits 7,296
The following is quoted from dv's post on 2003-7-9 1:38:48: findstr ？？？？？？？？？？？ Shouldn't it be the find command? Format: find "string" /? Maybe. You might be right. I don't know what the OP is talking about either. I'm just guessing. Hehe...

Floor5　Roy	Posted 2003-07-09 00:00
管理员　Posts 1,633　Credits 4,869
The following is quoted from dv's post on 2003-7-9 1:38:48: findstr ？？？？？？？？？？？ Shouldn't it be the find command? Format: find "string" /? I don't think so......... findstr is a Win2000/XP command........

Floor6　dv人	Posted 2003-07-09 00:00
初级用户　Posts 35　Credits 281
I remembered it wrong,,, there are find and findstr,,, and findstr is still more versatile,,, sorry for making a fool of myself -----------Searches for strings in files using literal text or regular expressions. Click "Related Topics" in the list for "Devinfo Help" to get a list of the regular expression symbols accepted by findstr. findstr filename ] Parameters /b Matches the pattern if it is at the beginning of a line. /e Matches the pattern if it is at the end of a line. /l Uses a literal search string. /c: string Uses the specified text as a literal search string. /r Uses the search string as a regular expression. This switch is not needed, because unless the /l switch is used, findstr interprets all metacharacters as regular expressions. /s Searches for matching files in the current directory and all subdirectories. /i Specifies that the search is case-insensitive. /x Prints lines that match exactly. /v Prints only lines that do not contain a match. /n Prints the line number before each matching line. /m If the file contains a match, prints only the file name. /o Prints the character offset before each matching line. /g filename Gets search strings from the specified file. /f file Reads the file list from the specified file. /d dirlist Searches the comma-separated directory list.

Floor7　buddiyar	Posted 2006-07-16 13:38
初级用户　Posts 75　Credits 160
set d="echo a.txt > b.txt" At this point the contents of b.txt are a.txt & copy %d% > 1.txt copy %d% becomes 1.txt & type 1.txt \| find /i "echo" > b.txt Search for the string echo in 1.txt; if found, write it into b.txt if not, it will be empty But note that what is used here is > So no matter how many echo strings there are in 1.txt the contents of b.txt will only be a single echo And here's another one, same effect as the one above prompt echo$Sb.txt$S$Gc.txt& echo z\|cmd\|findstr /e "t">b.txt

Floor8　IceCrack	Posted 2006-07-16 19:49
中级用户　Posts 168　Credits 332　From 天涯
set d="echo a.txt>b.txt" echo %d%>1.txt type 1.txt \| find /i "echo">b.txt Why is there such a big difference between having an & and not having one? Doesn't & just serve as a connector? I feel this should have the same effect as the OP's version. But in reality the effect is very different