egrepis non-standard and deprecated. Use
egrep 'foo|bar' file
grep -E 'foo|bar' file
egrep is a non-standard command. Its functionality is provided in POSIX by
grep -E. POSIX grep says:
This grep has been enhanced in an upwards-compatible way to provide the exact functionality of the historical egrep and fgrep commands as well. It was the clear intention of the standard developers to consolidate the three greps into a single command.
man grep for GNU says:
Direct invocation as either egrep or fgrep is deprecated
ShellCheck will fail to recognize when functions override
egrep. Consider giving it a different name or ignore this error.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.