replaceit.sh

#!/usr/bin/env bash

#####################################################
# Author: Shinichi Okada
# Version : v0.0.3
# Date: 2021-03-20
#####################################################

# Clean up
unset FROM TO dir_name

# set defaults
version="v0.0.3"
TO="_"
FROM=" "
work_dir=$(pwd)
file=""

usage() {
  cat <<EOF

Name: 
=====
replaceit

Description: 
============
This script replaces spaces of file names with underscores as the default.

Usage:  
======
replaceit [ -m FROM ] [ -t TO ]  
    -f  FROM (Default: space)
    -t  TO   (Default: _)
    -d  Directory name
    -o  One file replacement. Use quotes if the file has space(s).
    -h  Help

Examples:
=========
    The default changes from a space to _ of file names .
    $ replaceit  
    Change from - to _.
    $ replaceit -f - -t _
    Quote the file name when change one file with space(s).
    $ replaceit -o Downloads/test1.pdf 
    $ replaceit -o "Downloads/test 1.pdf"
    Using a directory
    $ replaceit -d mydir1
    Quote the directory name when it has space(s).
    $ replaceit -d "my dir 1"

EOF
  exit 2
}

###################
# main script

while (($# > 0)); do #while arguments count >0
  case "$1" in
  -f | --from)
    FROM=$2
    shift 2 # shift twice to bypass switch and its value
    ;;
  -t | --to)
    TO=$2
    shift 2 # shift twice to bypass switch and its value
    ;;
  -d | --dir)
    work_dir="$HOME/$2"
    shift 2 # shift twice to bypass switch and its value
    ;;
  -o | --one)
    file="$HOME/$2"
    shift 2 # shift twice to bypass switch and its value
    ;;
  -v | --version)
    echo $version
    exit 0
    ;;
  -h | --help | *)
    usage
    exit 0
    ;;
  esac
done

############# Main body ############

# check if work_dir exists
if [ ! -d "$work_dir" ]; then
  echo "Directory $work_dir doesn't exist."
  exit 1
fi

# -o flag is used to change only one file. Check if $file is not empty
if [ -n "$file" ]; then
  # check if $file is a file by -f exists
  if [ -f "$file" ]; then
    echo "We are replacing $FROM to ${TO} of ${file} file."
    new="${file//$FROM/$TO}"
    echo "$new"
    if [ "$new" != "$file" ]; then
      if [ -e "$new" ]; then
        echo "Not renaming $file because $new already exists"
        exit 2
      else
        echo "Moving one file $file to ${new}."
        mv "$file" "$new"
        exit 0
      fi
    fi
  else
    echo "No file found."
    exit 1
  fi
fi

echo
echo "=========="
echo "We are replacing $FROM to ${TO} in ${work_dir} directory."
echo "=========="
echo
for f in "$work_dir"/*; do
  # https://stackoverflow.com/questions/13210880/replace-one-substring-for-another-string-in-shell-script
  # To replace all occurrences, use ${parameter//pattern/string}
  # To replace the first occurrence of a pattern with a given string, use ${parameter/pattern/string}:
  new="${f//$FROM/$TO}"
  # echo "New: $new"
  # echo "Old: $f"
  if [ "$new" != "$f" ]; then
    if [ -e "$new" ]; then
      echo "Not renaming $f because $new already exists"
      exit 2
    else
      echo "- Moving $f in ${work_dir} to ${new}."
      mv "$f" "$new"
    fi
  fi
done

exit 0