02-05-2018
The second process, cmd2, will be able to read the standard output from cmd1 You should not need to know the PID.
It's all a bit theoretical at the moment. Can you explain what you really want to achieve?
Something like ls -l | more is a simple example of this. The output from ls -l (excluding errors) is passed to more which displays the output, pausing with a prompt when it believes it has written a screenful. The shell transfers the input for the more to be reading from the output of the ls rather than from the keyboard or whatever else standard input is defined as.
I'm sure we can explain this with a better example of what you are trying to do overall.
Kind regards,
Robin
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cat(1) General Commands Manual cat(1)
Name
cat - concatenate and print data
Syntax
cat [ -b ] [ -e ] [ -n ] [ -s ] [ -t ] [ -u ] [ -v ] file...
Description
The command reads each file in sequence and displays it on the standard output. Therefore, to display the file on the standard output you
type:
cat file
To concatenate two files and place the result on the third you type:
cat file1 file2 > file3
To concatenate two files and append them to a third you type:
cat file1 file2 >> file3
If no input file is given, or if a minus sign (-) is encountered as an argument, reads from the standard input file. Output is buffered in
1024-byte blocks unless the standard output is a terminal, in which case it is line buffered. The utility supports the processing of 8-bit
characters.
Options
-b Ignores blank lines and precedes each output line with its line number.
-e Displays a dollar sign ($) at the end of each output line.
-n Precedes all output lines (including blank lines) with line numbers.
-s Squeezes adjacent blank lines from output and single spaces output.
-t Displays non-printing characters (including tabs) in output. In addition to those representations used with the -v option, all tab
characters are displayed as ^I.
-u Unbuffers output.
-v Displays non-printing characters (excluding tabs and newline) as the ^x. If the character is in the range octal 0177 to octal 0241,
it is displayed as M-x. The delete character (octal 0177) displays as ^?. For example, is displayed as ^X.
See Also
cp(1), ex(1), more(1), pr(1), tail(1)
cat(1)