how to find a file in a directory linux code example

Example 1: find linux with extension

find /home/username/ -name "*.err"

Example 2: how to search in a directory files in linux

# this will search all subdirectories for text (no case sensitivity)
grep -inR "your text" .
# Node: this command will search for text INSIDE Files, not file names

Example 3: linux find file

# syntax 
# find *</path/to/dir> '(' *<Filter-1> *<and/or-operator> *<filter-2> ')'

# example 
find . '(' -name "Test*.pm" -a ! -name 'Useless*' ')'