Title here
Summary here
Command History
The Mysterious ^[[A
First, start a new Shell /bin/sh.
/bin/shThen enter the following command, everything is normal.
ls -lPress the up arrow key ⬆️ to view the previous command.
^[[AYou will find that you cannot see the previous command, instead, these characters ^[[A appear.
This is because early sh did not support viewing command history, until bash added this feature.
ANSI Escape Sequences
^[[A is an ANSI escape sequence, indicating the up arrow key.
^[：represents theEsckey (ASCII code 27), which is the start of the escape sequence.[A：represents the specific operation,[Aindicates the up arrow key.
When you press the up arrow key in the terminal, the terminal sends this character sequence ^[[A to the program,
usually used to call the previous command in the command history.
Since sh does not support viewing command history, it will output the character sequence of the key directly.
sh in Ubuntu
In Ubuntu, sh is actually a link to dash.
file /bin/sh/bin/sh: symbolic link to dashTherefore, dash also does not support viewing command history.
History Functionality
history Command
Without arguments, it outputs all history records.
historyYou can also use the short command, with the same effect.
!!.bash_history File
The persistent file for command history records.
-rw------- 1 kuga kuga 5516 Aug 24 08:23 /home/kuga/.bash_historyDuring the interaction with the Shell, the history records of the commands are saved in memory.
Using the history command can view the changes of the history records in real-time,
but the history records are only written to the .bash_history file when you exit the Shell.
If you want to write to the history record file immediately, you can use the following command.
history -aEnvironment Variables
HISTFILE
The path of the history record file.
echo $HISTFILE/home/kuga/.bash_historyHISTFILESIZE
The size of the history record file.
echo $HISTFILESIZE2000HISTSIZE
The size of the history record list in memory.
echo $HISTSIZE1000