Standard IO and redirection

1. Standard input/Output/error

When the shell starts, it inherits three files: stdin, stdout, stderr, standard input usually comes from the keyboard, standard output and standard error are usually screens.
Standard input/output/error file descriptors are 0, 1, 2

2. REDIRECT Operator

< REDIRECT input

<& redirect input, followed by a number format file descriptor

> REDIRECT Output

>> Append Output

2> REDIRECT Error

&> redirect error and output, followed by file name

>& redirect error and output, followed by file descriptor for file name or number format

2>&1 REDIRECT standard error to standard output

1>&2 REDIRECT standard output to standard error

>| Overwrite noclobber when redirecting output, that is, if file exists directly overwrite file

<>filename if it is a device file, use this file as standard input and standard output

3. Example

1) redirect standard error to file
$CC prog.c 2>errfile

2) redirect standard output to file, standard error redirect to empty device file
$CC prog.c >logfile 2>/dev/null

3) direct standard output and standard error to file or file descriptor
$CC prog.c &> logfile//must be a file name
$CC prog.c >& logfile//Can be file descriptor in file name or number format
$CC prog.c >& 1//redirect standard output and standard error to standard output, file descriptor for standard output is 1

4) redirect standard output to file, redirect standard error to standard output directed device
$CC prog.c >logfile 2>&1
is equivalent to
$CC prog.c >& LogFile

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Standard IO and redirection