Shell script to switch symbolic link

switch_symlink.sh

#!/bin/bash -e

# Directory that contains sources
SOURCE_DIR="/example/source"

# Directory to deploy sources to
TARGET_DIR="/example/bin"

# Directory to keep old generations
STAGING_DIR="/example/staging"

# Directory of the latest generation
LATEST_DIR="${STAGING_DIR}/$(date +%Y%m%d.%H%M%S)"

# Log file
LOG_FILE="/example/log/deploy.log"

function append_log () {
  if [ -d "$(dirname "$LOG_FILE")" ]; then
    tee -a "$LOG_FILE"
  else
    tee
  fi
}

function log_info () {
  echo "$(date --iso-8601=seconds) [deploy] $*" | append_log
}

function log_exec () {
  log_info "$@"
  "$@" 2>&1 | append_log
  if [ "${PIPESTATUS[0]}" -ne 0 ]; then
    false
  fi
}

log_info "Deploying..."

log_info "Copying sources into $LATEST_DIR"
log_exec mkdir -vp "$LATEST_DIR"
log_exec cp -vaT "$SOURCE_DIR" "$LATEST_DIR"

log_info "Updating symbolic link: $TARGET_DIR -> $LATEST_DIR"
log_exec ln -vs "$LATEST_DIR" "${TARGET_DIR}_tmp"
log_exec mv -vT "${TARGET_DIR}_tmp" "$TARGET_DIR"

log_info "Removing old generations..."
ls -t "$STAGING_DIR" | tail -n +5 | while read item; do
  log_exec rm -fr "$STAGING_DIR/$item"
done

log_info "Successfully deployed"