Solution to grep in bash

bash/grep/grep.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+
+# parsing CLI options
+while getopts :nlivx option; do
+    case "$option" in
+        # include line numbers in output
+        n) linenr=1 ;;
+        # only file names containing matching lines are printed
+        l) filename=1 ;;
+        # case insentivity
+        i) shopt -s nocasematch ;;
+        # matching lines are inverted (i.e., lines that do not match)
+        v) invert=1 ;;
+        # pattern should match whole line
+        x) entire=1 ;;
+        # other options are invalid and exit
+        \?) echo Invalid option.; exit 1;;
+    esac
+done
+
+# shifts the command-line arguments so that the remaining arguments
+# are just the pattern and the files to search in
+shift $((OPTIND-1))
+
+pattern=$1
+shift
+files=( "$@" )
+# if entire is set to 1, modifies the pattern to match the entire line
+# by anchoring it with ^ (beginning of line) and $ (end of line)
+(( entire )) && pattern="^$pattern$"
+
+for file in "${files[@]}"; do
+    count=0
+    while read -r line
+    do
+        (( count++ ))
+        out=
+        if (( invert )); then 
+            ! [[ ${line} =~ ${pattern} ]] && out="$line"
+        else
+            [[ ${line} =~ ${pattern} ]] && out="$line"
+        fi
+        # if filename is set to 1, prints the file name and breaks out
+        # of the loop after the first matching line in each file
+        if (( filename )) && [[ -n $out ]]; then
+            echo $file;
+            break;
+        fi
+        if (( linenr )) && [[ -n $out ]]; then
+            out="$count":$out;
+        fi
+        if (( ${#files[@]} > 1 )) && [[ -n $out ]]; then
+            out="$file":$out;
+        fi
+        [[ -n $out ]] && echo $out;
+    done < "$file"
+done 
+exit 0