One of the Bash shell basics

Bash Variable type:

Environment variables

Local variables (local variables)

Positional variables

Special variables

Local variable: Valid only in the current process (shell).

BASH: Direct use, no need to declare: Name = Jerry;

Variable substitution: How to reference a variable: ${variable}. Curly braces can be omitted most of the time, as in the above example, to use the values in a variable, echo$name.

Exception: double quotation marks (if referenced): for example, Name = pig, want to output there is some pigs need to write:

echo "There is some ${pig}s"

Single quotation mark (strong reference): in single quotes, even using ${pig},bash still does not use the data in the variable, but directly output ${pig}, the variable as a string.

Local variable scope: Entire bash process

Local variables: Local, valid only for the current code snippet

Environment variable: scope is the current shell process and its child processes

Export Varname=value

Positional variables: $1,$2, referencing script parameters

Special variables:

General program execution has two types of return values: execution result and execution state

$?: Saves the execution status return value of the previous command. Success for: 0, others for failure

Status: 1, 2,127: Command error. System reservation.

Output redirection:

> Overwrite redirects

>> Chasing heavier orientation

2> Error Overwrite redirect

2>> Error Append redirect

&> simultaneous redirection

Output redirection has a special location in the/dev/null: bit bucket. The data black hole can output any information inside.

ID student &>/dev/null The result of the command, regardless of the result of the failure or success, to the output here.

Undo variable: unset variable name

View variables: Set without any parameters

View current Environment variables: env or export

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One of the Bash shell basics