As the title. Hope experts can inform in the way of examples, and I am very grateful!
China DOS Union
Union site: www.cn-dos.net Forum site: www.cn-dos.net/forum
DOS stands for freedom, openness and progress. Let us work hard, learn from the openness and GNU spirit of FreeDOS and Linux, and together build and grow a free GNU GPL world!
中国DOS联盟论坛 » DOS批处理 & 脚本技术（批处理室） » Ask the expert to explain the symbols < and the command IF NOT defined!
View 1,556 Replies 6
Original Poster
Posted 2007-09-23 16:05 · 中国 山西 太原 电信
Floor 2
Posted 2007-09-23 18:00 · 中国 北京 海淀区 联通
Floor 3
Posted 2007-09-23 21:33 · 中国 重庆 电信
< represents input redirection
IF NOT defined means "if not defined"
IF NOT defined means "if not defined"
C:\>set a=1
C:\>if not defined a (echo yes) else (echo no)
no
Floor 4
Posted 2007-12-21 12:39 · 中国 安徽 马鞍山 电信
中级用户
★★
拟谷盗
Credits 312
Posts 108
Joined 2007-01-21 11:36
19-year member
UID 77238
Gender Male
Posts 108
Joined 2007-01-21 11:36
19-year member
UID 77238
Gender Male
Status Offline
Using `if not defined` can delete duplicate lines
for /f "delims=" %%i in (test.txt) do (
if not defined %%i set %%i=A & echo %%i>>test2.txt)
for /f "delims=" %%i in (test.txt) do (
if not defined %%i set %%i=A & echo %%i>>test2.txt)
Floor 5
Posted 2007-12-22 11:01 · 中国 广东 广州 电信
Originally posted by fbwolf at 2007-9-23 04:05 PM:
As the title suggests
I hope that the experts will inform me in an example way, and I am very grateful!
C:\>echo abcd>a.txt
C:\>set /p test=<a.txt
C:\>echo %test%
abcd
C:\>
C:\>set test=a
C:\>if defined test (echo Variable test exists) else (echo Variable test does not exist)
Variable test exists
C:\>if not defined test (echo Variable test does not exist) else (echo Variable test exists)
Variable test exists
C:\>set test=
C:\>if defined tset (echo Variable test exists) else (echo Variable test does not exist)
Variable test does not exist
C:\>if not defined tset (echo Variable test does not exist) else (echo Variable test exists)
Variable test does not exist
C:\>
Floor 6
Posted 2007-12-26 16:22 · 中国 北京 华为云
Finally understand some, thank you very much for the 5th floor!
Floor 7
Posted 2009-02-07 20:31 · 中国 北京 联通
Using `if not defined` can delete duplicate lines
for /f "delims=" %%i in (test.txt) do (
if not defined %%i set %%i=A && echo %%i>>test2.txt)
In the line `if not defined %%i set %%i=A & echo %%i>>test2.txt）`, the `&` should be `&&`.
for /f "delims=" %%i in (test.txt) do (
if not defined %%i set %%i=A && echo %%i>>test2.txt)
In the line `if not defined %%i set %%i=A & echo %%i>>test2.txt）`, the `&` should be `&&`.
Forum Jump: