Chapter 5

CREATING, VIEWING, AND EDITING TEXT FILES

STDIN, STDOUT, STDERR

NUMBER	CHANNEL NAME	DESCRIPTION	DEFAULT CONNECTION	USAGE
0	stdin	Standard input	Keyboard	read only
1	stdout	Standard output	Terminal	write only
2	stderr	Standard error	Terminal	write only
3+	filename	Other files	none	read and/or write

redirection	redirects
command > file	redirect and overwrite to file
command >> file	redirect and append to file
command 2> file	redirect stderr and overwrite file
command 2>/dev/null	redirect stderr to /dev/null
command > file 2>&1	1) redirect stdout and overwrite file, then 2) redirect stderr to stdout (same file) file contains both stdout and stderr
command &> file	same with above example
command >> file 2>&1	1) redirect stdout and append file, then 2) redirect stderr to stdout (same file) file contains both stdout and stderr
command &>> file	same with above example
command 2>&1 > file	1) redirect stderr to stdout (terminal), then 2) redirect stdout to file stderr prints to terminal, file only contains stdout

Redirectionu pipe ilə işlətdiyimiz vaxt, pipe-dan sonrakı komandaya stdin daxil olmur.

Bu kimi hallarçün tee işlətmək lazımdır. tee özündən əvvəlki komandadan gələn stdout-u stdin kimi qəbul edir, və özündən sonrakı pipe-a stdout kimi ötürür.

ls > file | less         # empty output
ls -l | tee file | less  # writes to file, prints to output

# Merge commands should not be used with pipe commands:
find / -name passwd 2>&1 | less # normal
find -name / passwd &> | less.  # syntax error
-bash: syntax error near unexpected token `|'

# adding /home/user/bin directory to PATH variable:
export PATH=${PATH}:/home/user/sbin

# to see currently set variables:
set

# to see all environment variables:
env

To set persistent variables look for these files:

/etc/profile
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc