Bash function that overcomes the limit of 32 files that `gsutil compose` can handle.

gcloud-compose-squish.sh

#!/bin/bash

# Based on:
# - https://stackoverflow.com/questions/66482517/how-to-append-more-than-33-files-in-a-gcloud-bucket#answer-66484002

GSUTIL="gsutil compose"
BATCH_SIZE="32"
BUCKET_BASE="gs://my-shiny-bucket/path/to/intermediate/composites"

# Will compose files in groups of maximum 32
# Ordered so that the last composite will contain all the previous files
# and will output to the last original parameter

function squish() {
  LST=("$@")
  LEN=${#LST[@]}

  if [ "${LEN}" -le "1" ]; then
    # Empty array; nothing to do
    return 0
  fi

  # Only unique for this configuration; be careful
  COMPOSITE=$(printf "${BUCKET_BASE}/composite-%04d" ${LEN})

  if [ "${LEN}" -le "${BATCH_SIZE}" ]; then
    # Batch can be composed with one command
    echo "${GSUTIL} ${LST[@]}"
    ${GSUTIL} ${LST[@]}
    return 0
  fi

  # Compose 1st batch of files
  # NB Provide start:size
  echo "${GSUTIL} ${LST[@]:0:${BATCH_SIZE}} ${COMPOSITE}"
  ${GSUTIL} ${LST[@]:0:${BATCH_SIZE}} ${COMPOSITE}

  # Remove batch from LST
  # NB Provide start (to end is implied)
  REM=${LST[@]:${BATCH_SIZE}}

  # Prepend composite from above batch to the next run
  NXT=(${COMPOSITE} ${REM[@]})

  squish "${NXT[@]}"
}

# Example run:
squish gs://bucket/key/file1.csv ... gs://bucket/key/file50.csv gs://bucket/key/merged.csv 

Using a specific filename to produce the final output, one could simply run a script like this to remove the intermediate files:

# Gets a list of every file that doesn't end with merged.csv
TO_BE_REMOVED=$(gsutil ls $BUCKET_BASE/ | sed 's/.*merged\.csv//' | xargs)

# And removes it
gsutil rm $TO_BE_REMOVED