Friday, January 8, 2016

How to delete a single command from history on a Linux, OS X and Unix Bash shell

 I'm working in Ubuntu bash terminal application and remotely on a RHEL server in cloud platform. I typed the wrong and dangerous command. I no longer wish to remember dangerous command in the history file. How can I remove or delete a single command from bash history file?

You can use the history command to clear all history or selected command line.

How do I view history with line number?

Simply type the history command:
$ history
Sample outputs:
Fig.01: Bash history command with line number on a Linux, OS X, and Unix
Fig.01: Bash history command with line number on a Linux, OS X, and Unix

How to delete a single command number 1013 from history

The syntax is:
## Delete the bash history entry at offset OFFSET ##
history -d offset
history -d number
history -d 1013
Verify it:
$ history

How do I delete all the history?

The syntax is:
history -c

Tip: Control bash history like a pro

First, you can increase your bash history size by appending the following config option in ~/.bashrc file:
## Set the  maximum  number of lines contained in the history file ##
## Set the number of commands to remember in the command history ##
## Append it ##
shopt -s histappend
# Controlling how commands are saved on the history file ##
# ignoreboth means:                       ##
# a) Command which begin with a space character are not saved in the history list               ##
# b) Command matching the previous history entry  to  not  be  saved (avoid duplicate commands) ##
Save and close the file.

Where to find more information about history command?

You can read bash man page by typing the following command:
$ man bash
Or simply type the following command:
$ help history
Sample outputs:
history: history [-c] [-d offset] [n] or history -anrw [filename] or history -ps arg [arg...]
    Display or manipulate the history list.
    Display the history list with line numbers, prefixing each modified
    entry with a '*'.  An argument of N lists only the last N entries.
      -c clear the history list by deleting all of the entries
      -d offset delete the history entry at offset OFFSET.
      -a append history lines from this session to the history file
      -n read all history lines not already read from the history file
      -r read the history file and append the contents to the history
      -w write the current history to the history file
     and append them to the history list
      -p perform history expansion on each ARG and display the result
     without storing it in the history list
      -s append the ARGs to the history list as a single entry
    If FILENAME is given, it is used as the history file.  Otherwise,
    if $HISTFILE has a value, that is used, else ~/.bash_history.
    If the $HISTTIMEFORMAT variable is set and not null, its value is used
    as a format string for strftime(3) to print the time stamp associated
    with each displayed history entry.  No time stamps are printed otherwise.
    Exit Status:
    Returns success unless an invalid option is given or an error occurs.

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