append-once

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append-once is a shell utility that appends a line to a file only once. It is useful for scripts that need to modify configuration files or other persistent files without introducing duplicate lines.

Introduction[edit]

append-oncearchive.org iconarchive.today icon:

  • Appends once and is supposed to avoid duplicating the same content, should the exact same lines have already been appended earlier.
  • Includes additional sanity testing (checks if the folder where the file resides is writable; checks if the file is readable and writable).
  • Offers an easier-to-use interface. [1]
  • Write operations are atomic.
  • Its write operation is similar to:
printf "%s\n" "text to append" | sponge -a /file/to/append/to >/dev/null

Target Audience[edit]

Info Advanced users only!

If append-once is used in security critical context it should only be used by people capable of reviewing its relatively short and is simple source code.

Syntax[edit]

append-once /path/to/file 'line to append'

Example[edit]

Click = Copy Copied to clipboard! append-once ~/testfile 'some text here'

Exit Codes[edit]

  • 0: Success.
  • Non-Zero: Failure.

Limitations[edit]

  • Did not support multi-line (with empty lines) at time of writing. Test before use.

Footnotes[edit]

  1. ↑ [1] No need to use:
    • grep
    • considering special characters in grep
    • printf
    • pipe
    • >/dev/null redirection.
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