Tricking bash HISTTIMEFORMAT

by Emile `iMil' Heitor - 2017-04-30

While trying to find a clean method to remove line numbers from the history command, I found an interesting trick by using the HISTTIMEFORMAT environment variable. Here’s what bash’s man says:

       HISTTIMEFORMAT
              If  this  variable  is  set and not null, its value is used as a
              format string for strftime(3) to print the time stamp associated
              with  each  history  entry displayed by the history builtin.  If
              this variable is set, time stamps are  written  to  the  history
              file  so they may be preserved across shell sessions.  This uses
              the history comment character  to  distinguish  timestamps  from
              other history lines.

But it turns out you can actually put pretty much anything in there, and for example, an ANSI escape sequence that does a line feed and erases the current line:

$ HISTTIMEFORMAT="$(echo -e '\r\e[K')"

There we go, no more line numbers:

$ history |tail -1
history |tail -1