Ubuntu – Half of bash history is missing

bashbash-historycommand line

The other night I was reading AU Q&A and used a bash command:

inxi -????

Problem is today I don't remember characters comprising ????. I want to put the command and parameters into my documentation spreadsheet. Based on an this answer (How to recall history in teminal) I used this command:

$ cat .bash_history | grep inxi
inxi -b
sudo apt install inxi
inxi -b

However the command I want isn't there even though the history goes far back. I've used the inxi commands many times in the terminal since that old history but none of is showing up.

I've also tried Ctrl+R+inxi without any luck. Because I open multiple terminal windows all the time is history tied to a specific window?

Is there a different way to grep bash history file(s)?

Note that I do not prefix terminal commands with a Space Bar such that they are supressed from history.

Best Answer

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
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