Bash Scripting – Troubles Piping Echo Output to xargs Script for mv Command

In one sentence: it doesn't work because you aren't calling it correctly.

First, since your script doesn't start with #!/bin/bash, it isn't actually a bash script. Which shell it is executed by depends on how you invoke it. When you invoke it from the bash command line, bash forks a new instance of itself (this has to happen to execute any external command anyway), and it's this new instance that executes the script. So the script is executed with the same settings (including the history so far) as the parent shell. It is executed with different options; in particular, history tracking is off for the commands in the script (which suits you, since otherwise it would add to the history that you want to modify).

Whether the bash instance executing the script has the HISTFILE variable set depends on whether it was exported in the parent (which is a little weird). If it isn't exported and thus set in the child, then the child script won't save the modified history when it ends.

If HISTFILE is exported, then the child script will modify your history file. However, unless you've configured your interactive shell to reload the history after every command, the modified history will only be picked up by newly started instances of bash.

If you want to run a shell snippet that affects the current shell instance, you must run that shell in the current shell instance, instead of running it as a subprocess. You'd run into a similar problem if you wanted to do other things that affect the shell process itself, such as changing directories, setting variables, etc. Use the . (“dot”) or source builtin to run a script in the current shell process.

. idelhistory 300 365

Alternatively, you could define this as a function in your .bashrc.

One difference is that when using command substitution instead of a pipe, the size of the data passed is limited by the size of the command buffer, so it is truncated in some cases with no warning. This also means that that the whole command output must be produced, and stored in memory, before it is passed to the next command, so for large outputs you can use much more memory than necessary.

Another issue with the first method is that the output is split on whitespace, so you can't handle filenames with spaces in them. xargs also is affected by the whitespace problem, but it can be fixed by changing the delimiter used. To properly handle filenames by the way, you would need to use the null byte as a delimiter in the second example.

A third issue is that globs are expanded, so if a file has asterisks or question marks in its name, there will be unexpected results.

You can find a nice discussion on the issue here: http://mywiki.wooledge.org/ParsingLs

The correct syntax would be

echo rm *

or if you must use xargs,

find . -maxdepth 1 -print0 | xargs -0 echo rm

Remove echo when the output looks correct.