Ubuntu – Hide “history -d” in bash history

bashbash-historycommand line

If I accidentally type my password or anything else sensitive in bash I can easily remove that line with history -d ROW#, but I'm always left with the history -d ROW# command in history showing everyone that someone corrected a mistake.

Can I append something to a command to prevent it from appearing in bash history?

Best Answer

To not save a single command in your history just precede it with a space (marked with ␣ here):

$ echo test
test
$ history | tail -n2
 3431  echo test
 3432  history | tail -n2
$ ␣echo test2
test2
$ history | tail -n2
 3431  echo test
 3432  history | tail -n2

This behaviour is set in your ~/.bashrc file, namely in this line:

HISTCONTROL=ignoreboth

man bash says:

HISTCONTROL
A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes ignorespace, lines which begin with a space character are not saved in the history list. A value of ignoredups causes lines matching the previous history entry to not be saved. A value of ignoreboth is shorthand for ignorespace and ignoredups.

ignoredups by the way is the reason why history | tail -n2 appears only once in the history in the above test.

A terminal's history is saved in the RAM and flushed to your ~/.bash_history as soon as you close the terminal. If you want to delete a specific entry from your ~/.bash_history you can do so with sed:

                                   # print every line…
sed '/^exit$/!d' .bash_history     # … which is just “exit”
sed '/^history/!d' .bash_history   # … beginning with “history”
sed '/>>log$/!d' .bash_history     # … ending with “>>log”
sed '\_/path/_!d' .bash_history    # … containing “/path/” anywhere

In the last one I changed the default delimiter / to _ as it's used inside the search term, in fact this is equal to sed -i '/\/path\//d' .bash_history. If the command outputs only the lines you want to delete add the -i option and change !d to d to perform the deletion:

                                   # delete every line…
sed -i '/^exit$/d' .bash_history   # … which is just “exit”
sed -i '/^history/d' .bash_history # … beginning with “history”
sed -i '/>>log$/d' .bash_history   # … ending with “>>log”
sed -i '\_/path/_d' .bash_history  # … containing “/path/” anywhere

Related Solutions

Ubuntu – How to find text and replace that line if exists with terminal otherwise just append line to end

You can use

sed 's/vm.swappiness=[0-9]*/vm.swappiness=1/g' /etc/sysctl.conf

If you don't mind how many digits your number has.

If you want a maximum of 3 digits, you need extended (modern) regular expressions rather than basic regular expressions (BRE's). You then need to provide the -E parameter

sed -E 's/vm.swappiness=[0-9]{1,3}/vm.swappiness=1/g' /etc/sysctl.conf

Ubuntu – Half of bash history is missing

I can't know what happened without access to your machine but here is a short explanation of how the history system works which might help you figure out what happened.

Each open terminal has its own history buffer. These buffers are appended to your $HISTFILE when the terminal is closed (maybe also whenever the buffer is filled, but I don't know how often that happens). Now, the way to search for a command in your history is to simply run:

history | grep command

But if the command was run in a different shell, you won't see it in the history of your current one. To fix that, you close all open shells, open a new terminal window and search your history again.

If that still doesn't help, you've probably passed the threshold of commands stored in the $HISTFILE. The behavior of the $HISTFILE is controlled by various environment variables (see man bash for the full list), but the relevant ones here are:

   HISTSIZE
          The  number  of commands to remember in the command history (see HISTORY below).  If the value is 0, commands are not saved in the history list.  Numeric values less than
          zero result in every command being saved on the history list (there is no limit).  The shell sets the default value to 500 after reading any startup files.

   HISTFILESIZE
          The maximum number of lines contained in the history file.  When this variable is assigned a value, the history file is truncated, if necessary, to contain no  more  than
          that number of lines by removing the oldest entries.  The history file is also truncated to this size after writing it when a shell exits.  If the value is 0, the history
          file is truncated to zero size.  Non-numeric values and numeric values less than zero inhibit truncation.  The shell sets the default value to the value of HISTSIZE after
          reading any startup files.

The higher values you set these to, the more commands you'll keep in your $HISTFILE. For example, I use:

HISTSIZE=999999
HISTFILESIZE=999999

If you want to import the history from one shell into another, you can use the history command:

$ help history | grep -E -- '-a|-r'
      -a    append history lines from this session to the history file
      -r    read the history file and append the contents to the history

So, run history -a to write the history from one terminal and then history -w to read it from the another. Now, running history will show you the history of both shells.

Finally, you can make all your terminals share the same history by adding these lines to your ~/.bashrc:

## history -a causes the last command to be written to the
## history file automatically and history -r imports the history
export PROMPT_COMMAND='history -a;history -r'

I also suggest you add this:

## Make Bash append rather than overwrite the history on disk:
shopt -s histappend

Best Answer

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Ubuntu – Half of bash history is missing

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