Blog/Bash Eternal History

2020-08-06: Bash Eternal History

Astronomers using NASA's Hubble Space Telescope have assembled a comprehensive picture of the evolving universe – among the most colorful deep space images ever captured by the 24-year-old telescope.

I often forget that special command I used a while back, so I use Bash history to find out what I did. The problem is that by default, the history is not very long.

The solution is simple. Enable an eternal bash history!

## file: ~/.bash_profile or ~/.bashrc
export HISTFILESIZE=
export HISTSIZE=
export HISTTIMEFORMAT="[%F %T] "

# Don't keep duplicate commands from filling up the history
export HISTCONTROL=erasedups
export HISTFILE=~/.bash_eternal_history

# save all commands to the history immediately instead of at logout, enables you to save history from multiple sessions at once.
PROMPT_COMMAND="history -a; $PROMPT_COMMAND"

So, to find something from your history you simply do

# history |grep btrfs
21726  [2020-08-04 19:56:10] btrfs fi us /mnt/6TB/
22074  [2020-08-06 12:41:26] btrfs fi df -s /mnt/systemRoot/snapshots/src.20200806T0001/
22075  [2020-08-06 12:46:28] btrfs fi du -s src.20200806T0001/
22076  [2020-08-06 12:47:56] btrfs fi du -s /media/usb-backup/volumes/src/src.20200806T0001/
22077  [2020-08-06 12:48:06] btrfs fi du -s /mnt/systemRoot/snapshots/src.20200806T0001/

And to execute one of the lines you do

# !21726
Overall:
    Device size:                   4.54TiB
    Device allocated:              3.50TiB
    Device unallocated:            1.04TiB
    Device missing:                  0.00B
    Used:                          3.47TiB
    Free (estimated):              1.06TiB      (min: 548.68GiB)
    Data ratio:                       1.00
    Metadata ratio:                   2.00
    Global reserve:              512.00MiB      (used: 0.00B)
    Multiple profiles:                  no

Data,single: Size:3.48TiB, Used:3.46TiB (99.61%)
   /dev/sdc2       2.19TiB
   /dev/sdb2       1.28TiB

Metadata,RAID1: Size:9.00GiB, Used:5.04GiB (56.02%)
   /dev/sdc2       9.00GiB
   /dev/sdb2       9.00GiB

System,RAID1: Size:32.00MiB, Used:416.00KiB (1.27%)
   /dev/sdc2      32.00MiB
   /dev/sdb2      32.00MiB

Unallocated:
   /dev/sdc2     534.67GiB
   /dev/sdb2     534.99GiB

GNU Bash manual

Forza (talk) 12:50, 6 August 2020 (UTC)