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Operating Systems Solaris cat file1 > file1
# 1  
Old 03-23-2010
cat file1 > file1
I have file1 with the contents
Code:
 
this is file1

when i do cat file1 , the output is

Code:
 
this is file1


when i run cat file1 > file1 , I receive the following message
Code:
 
cat: input file1 is output

now when i again do

cat file1 , all the contents are gone.

Can somebody explain what is happening?Smilie
# 2  
Old 03-23-2010
Basically you are overwriting the contents of the source file into the dest file where both the files are same.

Use different filenames
Code:
cat file1 > file2

# 3  
Old 03-23-2010
My question is , if i am overwriting the contents thaen i should see the overwritten contens . Why the file is becoming blank . I know that cat file1 > file2 will do the job
I want to know the logic behind this using concept of input and output streams
# 4  
Old 03-23-2010
The reason is simple: before cat is executed, the shell opens file1, and truncates it. Then cat opens file1 for reading, but it won't find any content as that's already gone.
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