Set file modification date from date stored as filename

Question

I have a lot of files where filename contains file creation date (IMG_YYYYMMDD_hhmmss.jpg):

IMG_20171015_133516.jpg
IMG_20171015_133827.jpg
IMG_20171015_142634.jpg
IMG_20171015_142834.jpg
IMG_20171015_142857.jpg

but actual file creation date is different. I need to set it back to date from a filename.

I know how to change the date of all files to current date:

find -type f -exec touch {} \;

and how to parse the file name to get the date in the proper format for touch -t

echo IMG_20171015_133516.jpg | awk -F_ '{print $2 substr($3,0,4) "." substr($3,5,2)}'
201710151335.16

But I have no idea how to combine these commands together to change all files.

find -type f -exec touch -t"$(echo '{}' | awk -F_ '{print $2 substr($3,0,4) "." substr($3,5,2)}')" {} \;

returns

touch: invalid date format ‘.’

Answer 1

In the shell:

for f in ./IMG_*.jpg ; do 
    t=${f##*/} 
    touch "$f" -t "${t:4:8}${t:13:4}.${t:17:2}"
done

Bash, ksh, zsh etc have the ${var:n:m} substring expansion, and if you need to do it recursively, enable globstar and use **/IMG_*.jpg instead.

Doing it with find needs the shell, too:

$ find -name "IMG_*.jpg" -exec bash -c '
  for f; do t=${f##*/}; touch "$f" -t "${t:4:8}${t:13:4}.${t:17:2}" ; done
  ' sh {} \+

The first argument to Bash after the script goes to the $0 variable, which usually contains the shell name. The rest go to the positional parameters $1, $2, etc. and for f or for f in "$@" loops over them. The construct is here is rather common (at least in unix.SE answers). The main part of the loop here is the same as in the first example.

---

The find command in your question find .. -exec touch -t"$(...)" {} \; doesn't work since the command substitution is in double quotes, so it gets expanded before find runs. The {} is piped literally to awk, and it just so happens that the awk script only prints a dot.

If you did put the command substitution in single quotes, it would be passed to touch as-is (find would only substitute {}). touch would get the argument -t$(echo ...), dollar signs, parenthesis and all. find doesn't run the command through the shell by itself, we need to explicitly do it, as above.

In single quotes example:

$ find -name x -exec echo 'hello $(foo {})' \;
hello $(foo ./x)