shell input and output

1. Read keyboard input

read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]

• -p prompt statement, followed by the message input
• -n number of characters, the length limit input
• -s shielding echo, typing on the screen is not displayed, generally used for password entry
• -t timeout, timeout waiting for input
• -d input limit encountered the symbol, the input termination
• -r shielded special characters \ escape function

$ read -s -t 5 -n 6 -p "Enter password: " password
$ echo $password

2. echo escape output

$ echo "hello\n world."
hello\n world.
$ echo -e "hello\n world."
hello
 world.

3. Redirection

Under normal circumstances, each Unix / Linux command is running will open three files:

• Standard input file (stdin): stdin file descriptor is 0, Unix default program data read from stdin.
• Standard output file (stdout): stdout file descriptor 1, Unix program default data output to stdout.
• The standard error file (stderr): stderr file descriptor 2, Unix program writes error information to stderr stream.

$ command < infile > outfile

Alternatively the input and output simultaneously, command <infile to redirect stdin to infile, then command> outfile redirect stdout, to the outfile.

(1) If you want to redirect stdout and stderr after the merger to file, write:

$ command > file 2>&1

(2) If you want to execute a command, but do not want to display the output on the screen, you can redirect the output to / dev / null:

$ command > /dev/null

/ Dev / null is a special file, its contents will be written to be discarded; if you try to read from the file, then nothing can not read.

(3) If you want to shield stdout and stderr, can be written:

$ command > /dev/null 2>&1