tar -r and -u: Append and Update (CI Errors)

tar -r appends new members and -u updates ones that changed.

Append and update let you add to an existing archive without rebuilding it, but they only work on uncompressed tar files, which trips up a lot of CI scripts.

What it does

tar -r (--append) adds the named files to the end of an existing archive. tar -u (--update) appends only files that are newer than the copy already in the archive. Both require a plain, uncompressed .tar, because tar cannot seek to the end of a gzip or zstd stream to append.

Common usage

Terminal

tar -rf archive.tar newfile.txt        # append a file
tar -rf archive.tar -C build extra/    # append from another dir
tar -uf archive.tar src/               # add only changed files

Options

Flag	What it does
-r / --append	Add files to the end of an archive
-u / --update	Append only files newer than the stored copy
-f <file>	The .tar to modify (must be uncompressed)
(note)	Update never deletes; old versions stay in the archive

Common errors in CI

tar: Cannot update compressed archives means you tried -r or -u on a .tar.gz; decompress first, append, then recompress, or rebuild the archive in one tar -c pass. Remember that -u does not replace members: it appends newer copies, so the archive can grow and extraction uses the last copy written.

Related guides

tar -c: Create an Archive (Usage & CI Errors)tar -c bundles files and directories into a single archive. Reference for the -c, -f, and -v flags plus the p… tar -z: gzip Compression (Usage & CI Errors)tar -z filters the archive through gzip for .tar.gz files. Reference for the -z flag plus the not-in-gzip-for… tar -t: List Archive Contents (Usage & CI Errors)tar -t prints the table of contents of an archive without extracting. Reference for -t and -v plus the format… tar -f: Naming the Archive File (Usage & CI Errors)tar -f tells tar which archive file to read or write, or to use stdin/stdout. Reference for the -f flag and t…