Shell I/O Redirection And Command tee

1. std I/O Code:

stdin:  0   #input read from keyboard on default
stdout:1   #info write 
stderr:2    #error write 
any   :n    #input or output from anywhere.
============================
1. [n] < $file or stdin  #read from $file or stdin to [n].
2. [n] > content.txt   #new write to content.txt
3. [n] >> content.txt   #append write to content.txt 
4. &> content.txt  

    >& content.txt  

   #same means of new write content.txt from stdout and stderr.  
============================
Examples:
$ ./test.sh >info.log   #stdout log to info.log
$ ./test.sh 1>info.log  #same as the above. 1> is same as >, 1 can be omited.
$ ./test.sh 2>error.log    #stderr error only to error.log, stdout info to screen

$ ./test.sh >& result.log  #stdout and stderr to result.log
$ ./test.sh &> result.log  #stdout and stderr to result.log
$ ./test.sh > result.log 2>&1 #stdout and stderr to result.log
$ ./test.sh 1> info.log 2>error.log #stdout to info.log, stderr to error.log

Omit: >/dev/null
$ ./test.sh >& /dev/null
$ ./test.sh &> /dev/null
$ ./test.sh > /dev/null 2>&1
$ ./test.sh 1> /dev/null 2>/dev/null 

2>&1: Means copy stdout to stderr. reference 1 in 2.
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2. To Screen And File Meanwhile By Command: tee

tee command reads the standard input and writes it to both the standard output and one or more files.

$ tee --help

Usage: tee [OPTION]... [FILE]...

Copy standard input to each FILE, and also to standard output.

  -a, --append              append to the given FILEs, do not overwrite

  -i, --ignore-interrupts   ignore interrupt signals

  -p                        diagnose errors writing to non pipes

      --output-error[=MODE]   set behavior on write error.  See MODE below

      --help     display this help and exit

      --version  output version information and exit

MODE determines behavior with write errors on the outputs:

  'warn'         diagnose errors writing to any output

  'warn-nopipe'  diagnose errors writing to any output not a pipe

  'exit'         exit on error writing to any output

  'exit-nopipe'  exit on error writing to any output not a pipe

The default MODE for the -p option is 'warn-nopipe'.

The default operation when --output-error is not specified, is to

exit immediately on error writing to a pipe, and diagnose errors

writing to non pipe outputs.

# copy stderr to stdout, and out to screen meanwhile result.log.

$ ./test.sh |& tee result.log 

$ ./test.sh 2>&1 | tee result.log 

#stderr to stderr.log, stdout to stdout.log. meanwhile to screen.

$ { { .test.sh | tee stdout.log 1>&3; } 2>&1 | tee stderr.log 1>&2; } 3>&1

#expression: 

  1>&3: rediection 1 to 3, temp setting stdout to &3, for display 3 to screen 

  2>&1 | tee: redirection 2 to 1, and tee to stderr.log