See the HISTCONTROL environment variable in bash (and maybe something similar in other shells): HISTCONTROL A colon-separated list of values contro

See the HISTCONTROL environment variable in bash (and maybe something similar in other shells): 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. [...] This is convenient because any time you don't want a command saved in history, just start it with a leading space. Also look at HISTIGNORE for finer grained control.