Rename files/directories in the current directory.

renamer.bash

#!/usr/bin/env bash
# Rename files/directories in the current directory.
# Unlike bash, sh doesn't implement [[ operator. Thus, the extension is intentionally set to .bash.　

# Help message
if [[ $1 == '' || $1 == '--help' || $2 == '' ]]; then
  {
    echo 'usage: renamer \033[3mpattern repl\033[0m\n'
    exit
  }
fi
# Safeguard: 
if [[ ${#1} -lt 3 ]]; then
  {
    echo "The \033[3mpattern\033[0m \"$1\" is too short: An extremely short \033[3mpattern\033[0m may cause unexpected pattern matching and destroy the filenames.\n"
    exit
  }
fi

n=0
for i in $(ls); do
    
    sub=$(echo $i | sed s/$1/$2/g)
    mv ${i} ${sub} 

    if [[ ${i} != ${sub} ]]; then
      echo 'Renamed:' ${i} '->' ${sub}
    fi

    # Emergency brake, just in case.
    if [[ $n -gt 1000 ]]; then
      break
    fi
    n=$(($n+1))

done
echo ''