SC2143 – ShellCheck Wiki

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Use grep -q instead of comparing output with [ -n .. ].

Problematic code:

if [ "$(find . | grep 'IMG[0-9]')" ]
then
  echo "Images found"
fi

Correct code:

if find . | grep -q 'IMG[0-9]'
then
  echo "Images found"
fi

Rationale:

The problematic code has to iterate the entire directory and read all matching lines into memory before making a decision.

The correct code is cleaner and stops at the first matching line, avoiding both iterating the rest of the directory and reading data into memory.

Exceptions

The pipefail bash option may interfere with this rewrite, since the if will now in effect be evaluating the statuses of all commands instead of just the last one. Be careful using them together.

ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.