Unix shell book

1. Basic Knowledge

CAT/etc/Shell
CHSH/bin/tcsh
Emacs = Vi?
Pdksh
Zsh

B C K
PID is 1 not 0

Home variables exists in passwd, And the last entry of passwd is sh.

PS-Ef svr4
PS au for BSD/Linux ps

Echo $ status
Echo $?

EUID // can be changed, like chown
EGID

Real UID/GID // from passwd file
// Owner. The root uid is 0.
Setuid
Setgid

Interestingly, umask is 000 by default, directory is 777 by default, and file is 666 by default. You can subtract two values.
For example, if umask is set to 022, directory is set to 755, and file is set to 644.
Umask is set in passwd.

CD-built-in-no fork

File descriptor
0 1 2 assigned

CSH is uncommon
Generally, no CSH is available.

PIPE is actually an operation between file discriptor.

 

Date -- help has two types: Command help and shell script.

For example, data + % H

 

CSH supports Yum install

 

$1

$ #

Finis

Common regular expressionsescape means switch from one to another ^ $ beginning of a line enchor doesn' t mean word start with it. notice: line beginning not sentence beginning. /</> beginning of word and end of Word

The second to the last one does not understand, and finally understands this command:/1, $/S/([0o] ccur /) ence // 1 rence/* is called wild card ..... date + % H is acceptable, but date + % H is not acceptable. classification command 2.1 grep