On startup, the history is initialized from the file named by the vari‐
able HISTFILE (default ~/.bash_history). The file named by the value
of HISTFILE is truncated, if necessary, to contain no more than the
number of lines specified by the value of HISTFILESIZE. When the his‐
tory file is read, lines beginning with the history comment character
followed immediately by a digit are interpreted as timestamps for the
preceding history line. These timestamps are optionally displayed