Bash 4.2 on CentOS 6.5:In my ~/.bash_profile I have a bunch of aliases, including:alias grep='grep -n --color=always'so that I can get color highlighting and print line numbers automatically when running grep. If I run the following, highlighting works as expected:$ grep -Re 'regex_here' *.pyHowever, when I ran this recently:$ find . -name '*.py' | xargs grep -E 'regex_here'the results were not highlighted and line numbers weren't printed, forcing me to go back and explicitly add -n --color=always to the grep command.Does xargs not read aliases in the environment?If not, is there a way to make it do that?
Have xargs use alias instead of binary
bash;alias;xargs
An alias is internal to the shell where it is defined. It is not visible to other processes. The same goes for shell functions. xargs is a separate application, which is not a shell, so doesn't have a concept of aliases or functions.You can make xargs invoke a shell instead of invoking grep directly. However just invoking a shell isn't enough, you have to define the alias in that shell as well. If the alias is defined in your .bashrc, you can source that file; however this may not work your .bashrc performs other tasks that don't make sense in a non-interactive shell.find . -name '*.py' | xargs bash -c '. ~/.bashrc; grep -E regex_here $@' _Beware of the intricacies of nested quoting when typing the regexp. You can simplify your life by passing the regexp as a parameter to the shell.find . -name '*.py' | xargs bash -c '. ~/.bashrc; grep -E $0 $@' regex_hereYou can perform the alias lookup explicitly. Then xargs will see grep -n --color=always.find . -name '*.py' | xargs ${BASH_ALIASES[grep]} regex_hereIn zsh:find . -name '*.py' | xargs $aliases[grep] regex_hereBy the way, note that find  | xargs  breaks on filenames containing spaces (among others). You can fix this by changing to null-delimited records:find . -name '*.py' -print0 | xargs -0 ${BASH_ALIASES[grep]} regex_hereor by using -exec:find . -name '*.py' -exec ${BASH_ALIASES[grep]} regex_here {} +Instead of calling find, you can do everything entirely inside the shell. The glob pattern **/ traverses directories recursively. In bash, you need to run shopt -s globstar to enable this glob pattern first.grep regex_here **/*.pyThis has a few limitations:If a lot of files match (or if they have long paths), the command may fail because it exceeds the maximum command line length.In bash 4.2 (but not in more recent versions, nor in ksh or zsh), **/ recurses into symbolic links to directories.Another approach is to use process substitution, as suggested by MariusMatutiae.grep regex_here <(find . -name '*.py')This is useful when **/ isn't applicable: for complex find expressions, or in bash 4.2 when you don't want to recurse under symbolic links. Note that this breaks on file names containing spaces; a workaround is to set IFS and disable globbing, but it's starting to get a bit complex:(IFS=$'\n'; set -f; grep regex_here <(find . -name '*.py') )