Defensive File Operations

Dry Run File Action

Preview or Apply

A dry-run flag lets a script show the intended file action before applying it. The same target can produce a preview or an apply plan.

Program

Play the script to choose dry-run mode and see the file action plan.

dry_run
dry_run_file_action.sh
Replay: real traced execution (multi-file project)
#!/usr/bin/env bash

dry_run=1
path="build/tmp"
if [ "$dry_run" -eq 1 ]; then
    action="would remove $path"
else
    action="remove $path"
fi
echo "$action"

#!/usr/bin/env bash

dry_run=0
path="build/tmp"
if [ "$dry_run" -eq 1 ]; then
    action="would remove $path"
else
    action="remove $path"
fi
echo "$action"

  1. dry_run ← 1

    3dry_run=14path="build/tmp"
    values this step1dry_run

  2. path ← build/tmp

    3dry_run=14path="build/tmp"5if [ "$dry_run" -eq 1 ]; then
    values this stepbuild/tmppath

  3. if [ "$dry_run" -eq 1 ]; then

    4path="build/tmp"5if [ "$dry_run" -eq 1 ]; then6    action="would remove $path"
    values this step1dry_run

  4. action ← would remove build/tmp

    5if [ "$dry_run" -eq 1 ]; then6    action="would remove $path"7else
    values this stepwould remove build/tmpactionbuild/tmppath

  5. echo "$action"

    9fi10echo "$action"
    outputwould remove build/tmp
    values this stepwould remove build/tmpaction

  1. dry_run ← 0

    3dry_run=04path="build/tmp"
    values this step0dry_run

  2. path ← build/tmp

    3dry_run=04path="build/tmp"5if [ "$dry_run" -eq 1 ]; then
    values this stepbuild/tmppath

  3. if [ "$dry_run" -eq 1 ]; then

    4path="build/tmp"5if [ "$dry_run" -eq 1 ]; then6    action="would remove $path"
    values this step0dry_run

  4. action ← remove build/tmp

    7else8    action="remove $path"9fi
    values this stepremove build/tmpactionbuild/tmppath

  5. echo "$action"

    9fi10echo "$action"
    outputremove build/tmp
    values this stepremove build/tmpaction
dry run A dry run previews the action without applying it.
apply mode Apply mode should be explicit and visible.
file action Destructive file actions are safer when the exact path is displayed first.