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Joachim Ansorg edited this page Nov 12, 2021 · 6 revisions

Use a ( subshell ) to avoid having to cd back.

Problematic code:

for dir in */
do
  cd "$dir"
  convert index.png index.jpg
  cd ..
done

Correct code:

for dir in */
do
  (
  cd "$dir" || exit
  convert index.png index.jpg
  )
done

or

for dir in */
do
  cd "$dir" || exit
  convert index.png index.jpg
  cd ..
done

Rationale:

When doing cd dir; somestuff; cd .., cd dir can fail when permissions are lacking, if the dir was deleted, or if dir is actually a file.

In this case, somestuff will run in the wrong directory and cd .. will take you to an even more wrong directory. In a loop, this will likely cause the next cd to fail as well, propagating this error and running these commands far away from the intended directories.

Check cds exit status and/or use subshells to limit the effects of cd.

Exceptions

If you set variables you can't use a subshell. In that case, you should definitely check the exit status of cd, which will also silence this suggestion.

ShellCheck

Each individual ShellCheck warning has its own wiki page like SC1000. Use GitHub Wiki's "Pages" feature above to find a specific one, or see Checks.

Clone this wiki locally