IO Redirection , IPC (Lec8,Lec09)

 

$ wc 0< /etc/passwd == redirecting filedescriptor 0 as /etc/passwd 

$ wc /etc/passwd == taking as cmd line argument

 

$ cat < file1 >file2  ==  $ cat >f2 <f1  ==  $ <f1 >f2 cat

per process file descriptor table (ppfdt) = file descriptor 0 as file1 , file descriptor 1 as file2

 

$ cp file1 file2 

$ cat <file1 >file2 == takes file1's content as input and spit it out to file2

 

$ cat 0<f1 1>op 2>err == if f1 doesn't exist the error message will pop out in terminal since ppfdt is still same as base case

$ cat f1 1>op 2>err == f1 is passed as command line argument since file descriptor 1,2 is alreay redirected error message will go to err file

 

for more explain == Bash One-Liners Explained, Part III: All about redirections (catonmat.net)

Bash One-Liners Explained, Part III: All about redirections

 

Inter Process Communication(IPC)

1. was very slow because it includes Disk IO

2. used Kernel Buffer, switching from user mode to kernel mode and vice versa take time

3. use shared memory , using systemV shared memory api 

 

pipe is manage by kernel

 

tee cmd

tee command takes standard input and wirte it on the disk(files) and stdout

Named Pipe

no data actually goes to fifo1 file , instead kernel creates pipe and redirect those input and oupt.

echo "something" > fifo1    ==   process is blocked

in the other terminal when we $ cat fifo1           we  can see "something" on screen and blocked process gets terminated