Summary of the Linux Learning Bash (ongoing ...)

Linux Summary bash features

1. Command history:
   2. Use command: History
   4. Environment variables:
      1. Histsize: The number of bars recorded in the command history buffer, which defaults to 1000;
      2. Histfile: Record the current logged-in user logout the history command to store files;
      3. Histfilesize: Command history file records the number of history, the default is 1000;
   6. Operation Command History:
      1. History d offset deletes the command histories for the specified line;
      2. History c empties the command in the historical buffer of the command;
      3. History # shows the most recent # commands from the past;
      4. History a manually appends the commands in the current session buffer to the historical file;
   8. To invoke a command in history:
      1. !#: Execute the # command repeatedly;
      2. !: Repeat the previous one (last command;)
      3. !string: Repeats the last command that begins with the specified string;
      4. Call the last parameter of the previous command:
         1. !$
         2. ESC,.

1. Control how the Command history is recorded:

   Environment variable: Histcontrol

   Three values:

   Ignoredups: Ignoring duplicate commands; the so-called repetition must be continuous and identical, including options and parameters;

   Ignorespace: Ignores all commands that begin with whitespace, not records;

   Ignoreboth: Ignore the above two items, both ignore the duplicate command, also ignore the beginning of the blank command;

How to modify environment variables:

Export variable name = "VALUE"

Or: Varname= "VALUE" Export VARNAME

1. Command completion:

   Internal command: Directly through the shell completion;

   External command: Bash searches for a file named for a given command from left to right, based on the path defined by the PATH environment variable, and is the command to be executed the first time it is found;

   Note: After the first search through path to the command, it will be stored in the hash cache, the next use no longer search path, from the hash to find;

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   TAB completion:

   If the user-given character is in the command search path and only one command matches it, the TAB key is directly complete;

   If the character entered by the user has more than one command in the command search path, the TAB key can be used to list the commands again;

1. Path Completion:

Begins with a string entered by the user as a path and searches the parent directory of its specified path for the file name beginning with the specified string;

If the only, then direct completion;

Otherwise, tab again to list all eligible paths and files;

1. Command line expansion:

1) ~: Expand to the user's home directory;

2) ~username: Expand the home directory for the specified user;

1. {}: Can host a comma-delimited list and expand it to multiple paths;

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1. Execution result status of the command:

   Success or failure;

   Bash uses a special variable $? Save the execution status result of the most recent command;

   Value: 0: Success;

   1-255: Failure, 1,127,255 for system retention;

   Program execution has two types of results:

   The return value of the program, the output of the execution of the program itself;

   The execution status result of the program;

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1. Command Aliases (alias)
   1. Implemented by the alias command:
      1. Alias displays all the available command aliases for the current shell process;
      2. Define alias: Alias Name= ' VALUE ' defines the alias name, which executes equivalent to executing the command value,value can contain commands, options, parameters;
      3. To define a command alias by modifying the configuration file:

      Current User: ~/.BASHRC

      Global Users:/ETC/BASHRC

The bash process re-reads the configuration file:

Source/path/to/config_file

． /path/to/config_file

Revoke alias: Unalias

Unalias [-A] name [name ...]

Note: For commands that define aliases, use the original command to use the \command

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1. Glob (globing)

Used in bash to implement file name "wildcard"

Wildcard characters: *,? ，[]

1. * Arbitrarily from any character of length;

   A*b:

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2. ? any single character;

   A?b:

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3. [] matches any single character within the specified range;

   [0-9] [A-z] is case insensitive

   [admin] can be in the form of an interval, or it can be discrete;

4) [^] matches any character outside the specified range;

[^0-9] Any character of a single non-digit;

Dedicated Character Set:

[:d igit:] Any single number equivalent to [0-9]

[: Lower:] Any single lowercase letter,

[: Upper:] any single capital letter;

[: Alpha:] Any single case of uppercase and lowercase letters;

[: Alnum:] any number or letter;

[: space:] any white space character;

[:p UNCT:] any single special character;

Note: When using [] to reference a dedicated character set, the outer layer also needs to be nested []. For example:

# ls-d/etc/l*[[:d igit:]]*[[:lower:]]

1. Bash shortcut keys: