Useful for renaming a bunch of files that include date stamps in their names

update-date.sh

#!/bin/bash

# Default flag values
VERBOSE=false
WHAT_IF=false

# Parse flags and arguments
ARGS=()
while [[ $# -gt 0 ]]; do
    case "$1" in
        --verbose|-v)
            VERBOSE=true
            shift
            ;;
        --whatif)
            WHAT_IF=true
            shift
            ;;
        -*)
            echo "Error: Unknown option $1" >&2
            exit 1
            ;;
        *)
            ARGS+=("$1")
            shift
            ;;
    esac
done

# Ensure we have exactly two main arguments (old_date and new_date)
if [ ${#ARGS[@]} -ne 2 ]; then
    echo "Usage: $(basename "$0") [--verbose] [--whatif] <old_date> <new_date>"
    echo "Example: $(basename "$0") --whatif 260728 260619"
    exit 1
fi

OLD_DATE="${ARGS[0]}"
NEW_DATE="${ARGS[1]}"

# Counter to track modified files
count=0

# Loop through all files in the current directory matching the OLD_DATE prefix
for file in "${OLD_DATE}"*; do
    # Ensure the glob matched a real file
    if [ ! -f "$file" ]; then
        if [ "$count" -eq 0 ]; then
            echo "No files found starting with '${OLD_DATE}'."
        fi
        break
    fi

    # Replace ONLY the leading OLD_DATE prefix with NEW_DATE
    new_file="${NEW_DATE}${file#$OLD_DATE}"

    # Perform rename (or simulate)
    if [ "$WHAT_IF" = true ]; then
        echo "[What If] Would rename: '$file' -> '$new_file'"
    else
        if [ "$VERBOSE" = true ]; then
            echo "Renaming: '$file' -> '$new_file'"
        fi
        # -n prevents accidental overwrites if a file with new_file name exists
        mv -n "$file" "$new_file"
    fi

    ((count++))
done

if [ "$WHAT_IF" = true ]; then
    echo "Done. Processed $count file(s) in preview mode."
elif [ "$VERBOSE" = true ]; then
    echo "Done. Renamed $count file(s)."
fi