mjhjmtu

For the purpose of testing, I'd like count how many images files are inside a directory, separating each image file type by file extension (jpg="yes". This because later it will be useful for another script that will execute an action on each file extension). Can I use something like the following for only JPEG files?

jpg=""
count=`ls -1 *.jpg 2>/dev/null | wc -l`
if [ $count != 0 ]
then
echo jpg files found: $count ; jpg="yes"
fi

Considering file extensions jpg, png, bmp, raw and others, should I use a while cycle to do this?

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=( *."$ext" )
 printf 'number of %s files: %dn' "$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.

My approach would be:

1. List all files in the directory


2. Extract their extension


3. Sort the result


4. Count the occurrences of each extension

Sort of like this (last awk call is purely for formatting):

ls -U | awk -F . 'print $NF' | sort | uniq -c | awk 'print $2,$1'

This recursively traverses files and counts extensions that match:

$ find . -type f | sed -e 's/.*.//' | sort | uniq -c | sort -n | grep -Ei '(tiff|bmp|jpeg|jpg|png|gif)$'
 6 tiff
 7 bmp
 26 jpeg
 38 gif
 51 jpg
 54 png

find -type f | sed -e 's/.*.//' | sort | uniq -c

Anything involving ls is likely to produce unexpected results with special chars (space and other symbols). Any bashism (like arrays) isn't portable. Anything involving while read is usually slow.

On the other hand, find is VERY flexible (lots of options to filter), it has [at least] two syntax which are fail safe for special chars... and It scales well on large directory.

For this example, I have used -iname to match both upper and lower case extension name. I have also restricted the -maxdepth 1 to respect your question's "in current directory". Rather than counting the number of lines, where filenames could include CR/LF, -print0 will print a NULL byte at the end of each filename... so | tr -d -c "00" | wc -l is accurately counting files (NULL bytes!).

extensions="jpg png gif"
for ext in $extensions; do
 c=$(find . -maxdepth 1 -iname "*.$ext" -print0 | tr -d -c "00" | wc -c)
 if [ $c -gt 0 ]; then
 echo "Found $c *.$ext files"

 find . -maxdepth 1 -iname "*.$ext" -print0 | xargs -0 -r -n1 DOSOMETHINGHERE
 # or # find . -maxdepth 1 -iname "*.$ext" -exec "ls" "-l" "" ";"
 fi
done

P.S. -print0 | tr -d -c "00" | wc -c can be replaced with -printf "00" | wc -c or even -printf 'n' | wc -l.

Maybe it can get shorter

exts=( *.jpg *.png *.gif ); printf "There are $#exts[@]" extensions;

can just use ls for something this simple IMO

ls -l /opt/ssl/certs/*.pem | wc -l

or

count=$(ls -l /some/folder/*.jpg | wc -l)