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I have some commands in my Bash history that I want to remove.

I can find them with history | grep "command with password" then remove them with history -d <line-number>

However, when I try to delete them in bulk by piping them to xargs like this I get an error:

history | grep "command with password" | awk '{print $1}' | sort -r | xargs history -d
xargs: history: No such file or directory

I thought that xargs would go through the list of line numbers and send it one by one to the history -d command.

What is causing this error?

NB: I know there are other ways to delete the history, the question is purely to improve my understanding of how xargs works and what I am doing wrong that is causing the error.

Jeff Schaller
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opticyclic
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1 Answers1

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The error is raised because xargs cannot find a history command. It is a shell builtin, as you can confirm with type history, thus not visible to xargs. Try

echo 1 | xargs history -d; echo $?

The return value is 127. In man xargs, EXIT STATUS section:

0 if it succeeds
123 if any invocation of the command exited with status 1-125
124 if the command exited with status 255
125 if the command is killed by a signal
126 if the command cannot be run
127 if the command is not found
1 if some other error occurred.

Expanding on ilkkachu's comment, in principle you could invoke Bash and call history from the spawned shell.

echo 1 | xargs -I {} bash -c 'echo $HISTFILE; history' bash {}

The above command does not raise an error, after all the builtin history is available to the Bash shell. However, from that same command one also finds that HISTFILE is unset and history outputs nothing: The history is not enabled on a non-interactive shell. Again, you could activate it with the set builtin, export HISTFILE and HISTFILESIZE... But we don't want a headache. Editing .bash_history directly is the straightforward way to go.

Quasímodo
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    Very interesting. I never knew that xargs couldn't call shell builtins! – opticyclic Jul 19 '20 at 20:33
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    @opticyclic, it could, if it used a shell to start the programs, instead of doing it itself. And you can do it anyway with something like xargs sh -c 'some shell code' sh. It just wouldn't help because that copy of the shell might have a different concept of the history than the main shell where you started the whole pipeline – ilkkachu Jul 19 '20 at 20:49
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    @opticyclic It is a bit surprising at the first moment, but if you think about it, how would xargs decide on which shell to look for builtins? bash, ksh, dash, zsh? It seems reasonable that it doesn't go as far as that. – Quasímodo Jul 19 '20 at 20:57
  • Both comments totally make sense. Very useful in helping my understanding! – opticyclic Jul 19 '20 at 21:08
  • @opticyclic: xargs isn't a shell-builtin itself so it runs in a separate process. If you wanted to do something like it, you might write a shell loop that used while read, or bash array variables and iterate over them, or some other pure shell construct that can run commands inside the current shell. – Peter Cordes Jul 20 '20 at 04:53
  • @Quasímodo, it would probably use /bin/sh. (or on the more weird systems, some other path where it knows a POSIX shell is available; if /bin/sh isn't one.) Or perhaps what's in the user's SHELL, possibly. – ilkkachu Jul 20 '20 at 07:47
  • "Editing .bash_history directly is the straightforward way to go." -- well, except that if the command is in the history of a running shell (only), it only gets written to $HISTFILE when the shell exits, so it might not be there to be removed yet. Though if the shell has read some history from $HISTFILE, and you then remove the lines from the file, at least the shell doesn't seem to write them back. But if you have something already in $HISTFILE, and use history -d , it doesn't seem to delete it from the file. So, what you want to do depends on where the command is already stored. – ilkkachu Jul 20 '20 at 09:30
  • For those wondering, history can work under xargs by forcing an interactive shell and setting the history option in bash: echo 1 | xargs -i bash -ci 'set -o history; echo $HISTFILE; history' _ {}. But as others pointed out, it may be preferable to edit the file itself. – fzbd Jul 20 '20 at 10:13
  • @fzbd, and just to repeat the point I made above until it sticks, ___that doesn't work for removing anything from the history file___. It's not just "preferable" to edit the file itself, or to do something other than that, it's necessary. – ilkkachu Jul 20 '20 at 11:08
  • @ilkkachu "preferable" depends on the user's intended task. If they just want to modify the current shell session history, my comment shows how to access it in xargs, which was one of the points from OP (i.e. "improve my understanding of how xargs works"). If they want to remove it persistently, they edit the file instead of using the history builtin. Hope that clears any confusion. – fzbd Jul 20 '20 at 11:51
  • @ilkkachu Thank you for your important remarks. Particularly: "If the command is in the history of a running shell (only), it only gets written to $HISTFILE when the shell exits". In which case the reader should refer to Chris Down's answer in the linked question. – Quasímodo Jul 20 '20 at 12:12
  • @ilkkachu I guess I wasn't clear, but by "current shell session" I meant the one started by xargs, of course it will be distinct from the shell session that starts xargs. My point still stands that history operations are possible to do under xargs, and it is suitable for the purpose of understanding the behaviour of interactive vs non-interactive shells regarding bash builtins. – fzbd Jul 20 '20 at 14:15