Bash – How to do more than one substring replace at once in bash

bashreplaceshell-script

I have a directory contains image files that are to be echoed in bash. While echoing, I want to replace both file name and extension in single line command.

Example files:

images/file_name_1.jpg
images/file_name_2.jpg

Normally, I can do single replacement like this:

for i in images/*; do echo ${i/file/image}; done

And the output becomes like:

images/image_name_1.jpg
images/image_name_2.jpg

How can I keep it in for loop and replace the "jpg" string to "png" also? It's just an instance, I could replace the dot to comma etc.

When I try this:

for i in images/*; do echo ${{i/jpg/png}/file/image}; done

It doesn't work. I coulnd't find any other solution or idea. Is this possible -if so, how?

Best Answer

The simple approach would be to assign the result to a variable, then work with that variable. Example:

for filename in images/*
do
    echo "filename is now $filename"
    filename=${filename/jpg/png}; echo "filename is now $filename"
    filename=${filename/file/image}; echo "filename is now $filename"
    echo "final filename is ${filename}"
done

Related Solutions

Bash – For each subfolder, sort files by name and rename them to sequential padded numbers (regardless of extension)

for dir in */*; do           # loop over the directories
    (                        # run in a subshell ...
        cd "$dir"            # ... so we don't have to cd back
        files=(*)            # store the filenames in a zero-indexed array

        for index in "${!files[@]}"; do
            file=${files[$index]}
            ext=${file##*.}
            newname=$(printf "%02d.%s" $((index+1)) "$ext")
            mv "$file" "$newname"
        done
    )
done

Suppose you have a file with no extension. In that case it will have the same name except with leading numbers (e.g. my_file => 05.my_file)

All non-hidden directory entries will be renamed, including directories.

Shell Script – Count Files in a Directory by Extension

I'd suggest a different approach, avoiding the possible word-splitting issues of ls

#!/bin/bash

shopt -s nullglob

for ext in jpg png gif; do 
  files=( *."$ext" )
  printf 'number of %s files: %d\n' "$ext" "${#files[@]}"

  # now we can loop over all the files having the current extension
  for f in "${files[@]}"; do
    # anything else you like with these files
    :
  done 

done

You can loop over the files array with any other commands you want to perform on the files of each particular extension.

More portably - or for shells that don't provide arrays explicitly - you could re-use the shell's positional parameter array i.e.

set -- *."$ext"

and then replace ${#files[@]} and ${files[@]} with $# and "$@"

Best Answer

Related Solutions

Bash – For each subfolder, sort files by name and rename them to sequential padded numbers (regardless of extension)

Shell Script – Count Files in a Directory by Extension

Related Question