ok i need help understanding the following points in the command by radoulov
1.why was rm f1 issued and then && applied?

2.which redirection has precedence over the other? < one first , or > one first? according to me output redirection(>) should run first because, its inside the { } ... but i dont think i am right...

3. cat - f2 <f1 i understood, but i could'nt grasp the order in which the commands would execute?
to further explain my confusion....this is what i could make out of the command

Code:

[c_d@localhost pipesnfilters]$ { rm f1 && cat - f2 | sort -u >f1 ; } <f1

here, the code inside the brackets gets executed first, but first since redirection takes precedence - is read from f1 . then a logical is performed between the outputs of rm f1 and cat - f2? I am not really sure of that though...because replacing && with ; also works. so i think its executing 2 different commands one after the other, instead of performing a logical operation...please clarify whats happening here....

{ rm f1 && cat - f2 ; } <f1 gives the following output...

Code:

[c_d@localhost pipesnfilters]$ { rm f1 && cat - f2 ; } <f1
this is file1
the quick brown fox jumped over the lazy dog
this is file1
who let the dogs out
this is unix
this is file1

this is file2

with file f1 deleted
and this is piped with sort -u so , the repeated lines would be eliminated...

Code:

[c_d@localhost pipesnfilters]$ { rm f1 && cat - f2 | sort -u ;} <f1

the quick brown fox jumped over the lazy dog
this is file1
this is file2
this is unix
who let the dogs out

then you are redirecting the output to f1 using >f1 it does not matter what the contents of f1 , as f1 is removed...

please correct me... clearly i m very confused...
how is it that in this version <f1 percedes >f1???? and no matter however i try to manipulate this command i get the wrong output?



when you say exec's "somecommand" you dont mean the exec command do you,you meant executes "somecommand" didnt you? ofcourse you dont...but if at all you do, then i did not understand your clarification...if you didnt then i did...