Shell Scripting Learning

To see what versions of the Shell:cat/etc/shells system are currently running, the first process that starts is init

How bash Shell debugs:
Simply add parameters after the SH command
-N: Do not execute scripts, query the grammar within the scripts, if there are errors are listed!
-V: The contents of scripts are displayed on the screen before executing the scripts;
-x: The scripts content that will be used is displayed on the screen, slightly different from-V!

Operational symbols represent meaning
= equals
! = does not equal
< less than
> Greater than
-eq equals
-ne Not equal to
-lt less than
-GT Greater than
-le less than or equal to
-ge greater than or equal to
-A both are established (and)
-O unilaterally established (or)
-Z Empty string
-N Non-empty string

Export command: Turn custom variables into environment variables
Note: Child processes do not inherit custom variables from the parent process

Shell Scripting Learning