Overview of history
Every time a user enters a command in the terminal, that command is recorded in a history file (usually `~/.bash_history` or `~/.zsh_history`). The `history` command reads the contents of this file and displays it on the screen, and the history is preserved even after the shell session ends.
Main Roles of history
The `history` command is primarily used for the following purposes:
Key Use Cases
- Re-executing commands: You can easily re-execute long commands used previously without needing to retype them.
- Tracking tasks: It helps to check what tasks were performed in the past and understand the workflow.
- Improving productivity: Quickly find frequently used commands, saving input time.
- Reference for script writing: Utilize combinations of commands that were successfully executed in the past for script writing.
Environment Variables and history
The history functionality is influenced by several environment variables:
Key Related Environment Variables
- `HISTSIZE`: The maximum number of command history entries to be stored in memory. It is retained during the current shell session.
- `HISTFILESIZE`: The maximum number of command history entries to be stored in the history file (e.g., `~/.bash_history`). It is preserved between shell sessions.
- `HISTFILE`: Specifies the path of the file where command history is stored. The default is `~/.bash_history`.
- `HISTCONTROL`: Controls the way history records are maintained. (e.g., `ignoredups` - ignore duplicate commands, `ignorespace` - ignore commands that start with a space)
Key history Command Options
The `history` command provides various options necessary to query, modify, and manage the history list.
1. Viewing and Outputting History
2. Modifying and Re-executing History
Generated command:
Try combining the commands.
Description:
`history` Executes the command.
Combine the above options to virtually execute commands with AI.
Usage Examples
Learn how to effectively query and reuse command history through various examples of the `history` command.
View the Last 20 Commands
history 20Outputs a list of the 20 most recently executed commands along with their numbers.
Search for Specific String in Command History
history | grep dockerUse the `grep` command to find commands containing 'docker' in the `history` history.
Re-execute Previous ls Command
!lsFinds and re-executes the most recently executed command starting with `ls`.
Reuse Last Argument of Last Command
cat /var/log/syslog
less !$Useful when you want to reopen `/var/log/syslog` with the `less` command after executing `cat /var/log/syslog`.
Immediately Save Current Shell History to File
history -wImmediately save all commands executed in the current session to the `~/.bash_history` file before closing the shell.
Delete Specific History Entry Number
history -d 125Deletes the command with number 125 from history when checked using the `history` command. (Note: Once deleted, it cannot be recovered)