GH-50917: [C++] Fix shellcheck errors in cpp/build-support/*-flatbuffers.sh

[hiroyuki-sato]

Rationale for this change

This is the sub issue #44748.

• SC2034: foo appears unused. Verify it or export it.
• SC2207: Prefer mapfile or read -a to split command output (or quote to avoid splitting).
• SC2086: Double quote to prevent globbing and word splitting.

shellcheck cpp/build-support/*flatbuffer*.sh

In cpp/build-support/update-flatbuffers.sh line 27:
PYTHON_SOURCE_DIR="$CWD/../../python"
^---------------^ SC2034 (warning): PYTHON_SOURCE_DIR appears unused. Verify use (or export if used externally).


In cpp/build-support/update-flatbuffers.sh line 29:
TOP="$FORMAT_DIR/.."
^-^ SC2034 (warning): TOP appears unused. Verify use (or export if used externally).


In cpp/build-support/update-flatbuffers.sh line 33:
FILES=($(find $FORMAT_DIR -name '*.fbs'))
       ^-- SC2207 (warning): Prefer mapfile or read -a to split command output (or quote to avoid splitting).
              ^---------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
FILES=($(find "$FORMAT_DIR" -name '*.fbs'))


In cpp/build-support/vendor-flatbuffers.sh line 28:
mkdir -p $VENDOR_LOCATION
         ^--------------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
mkdir -p "$VENDOR_LOCATION"


In cpp/build-support/vendor-flatbuffers.sh line 29:
cp -f $FLATBUFFERS_HOME/include/flatbuffers/base.h $VENDOR_LOCATION
      ^---------------^ SC2086 (info): Double quote to prevent globbing and word splitting.
                                                   ^--------------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
cp -f "$FLATBUFFERS_HOME"/include/flatbuffers/base.h "$VENDOR_LOCATION"


In cpp/build-support/vendor-flatbuffers.sh line 30:
cp -f $FLATBUFFERS_HOME/include/flatbuffers/flatbuffers.h $VENDOR_LOCATION
      ^---------------^ SC2086 (info): Double quote to prevent globbing and word splitting.
                                                          ^--------------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
cp -f "$FLATBUFFERS_HOME"/include/flatbuffers/flatbuffers.h "$VENDOR_LOCATION"


In cpp/build-support/vendor-flatbuffers.sh line 31:
cp -f $FLATBUFFERS_HOME/include/flatbuffers/stl_emulation.h $VENDOR_LOCATION
      ^---------------^ SC2086 (info): Double quote to prevent globbing and word splitting.
                                                            ^--------------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
cp -f "$FLATBUFFERS_HOME"/include/flatbuffers/stl_emulation.h "$VENDOR_LOCATION"

For more information:
  https://www.shellcheck.net/wiki/SC2034 -- PYTHON_SOURCE_DIR appears unused....
  https://www.shellcheck.net/wiki/SC2207 -- Prefer mapfile or read -a to spli...
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...

What changes are included in this PR?

• SC2034: Comment out unused variables
• SC2207: Populate arrays without command substitution
• SC2086: Quote variables

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

• GitHub Issue: [C++] Fix shellcheck errors in cpp/build-support/*-flatbuffers.sh #50917

[github-actions]

⚠️ GitHub issue #50917 has been automatically assigned in GitHub to PR creator.

[hiroyuki-sato]

@kou As I mentioned before, these files are not referenced anywhere in this project. Could you tell me how to test it?

[kou]

See:

arrow/cpp/build-support/update-flatbuffers.sh

Line 21 in 1188927

# Run this from cpp/ directory. flatc is expected to be in your path

arrow/cpp/build-support/vendor-flatbuffers.sh

Lines 23 to 24 in 1188927

	# Run this from cpp/ directory with $FLATBUFFERS_HOME set to location of your
	# Flatbuffers installation

[hiroyuki-sato]

Thanks.

I confirmed this change by running the following commands in the cpp directoy.

./build-support/update-flatbuffers.sh
FLATBUFFERS_HOME=/opt/homebrew/Cellar/flatbuffers/25.12.19/ ./build-support/vendor-flatbuffers.sh

[kou]

+1

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit 2c35b59.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 1 possible false positive for unstable benchmarks that are known to sometimes produce them.