Execution process in pipeline

Question

This code shows nothing(if date.txt does exist):

date > date.txt | cut < date.txt --delimiter ' ' --fields 1

Questions:

• Why can't we use date.txt if we have redirected stdout in it?
• Is it like cut takes date.txt as input before it getting written/overwritten? Is the command execution sequence is from left to write in a pipeline or all commands get executed simultaneously and just wait for stdin from stdout of previous pipe command?

[apologies for grammar and terminology mistakes, and

date |tee date.txt | cut --delimiter ' ' --fields 1

works, it is known.

]

Answer 1

Commands in a pipeline are executed concurrently. So when you write

date > date.txt | cut --delimiter '' --fields 1 < date.txt

cut might try to read from the file before date has written to it, and there's nothing to read. There's no need for a pipeline if you're using a file for communication, just write the commands sequentially.

date > date.txt 
cut --delimiter '' --fields 1 < date.txt