gzcmp

gzcmp [cmp-or-diff-options] file1 [file2]

file1
    The first file to be compared. This can be an uncompressed file or a gzip-compressed file (typically ending in .gz).

file2
    The second file to be compared. Like file1, it can be uncompressed or gzip-compressed. If this argument is omitted, gzcmp will attempt to compare file1 (assuming it ends with .gz) with its uncompressed counterpart (e.g., comparing archive.gz with archive).

[cmp-or-diff-options]
    Options and arguments provided here are directly passed through to the underlying cmp or diff command used for the actual content comparison. gzcmp itself does not define unique command-line options.

gzcmp is a utility designed for the byte-by-byte comparison of two files, where at least one is typically compressed with gzip. It operates by transparently decompressing the files on the fly and piping their uncompressed content to the standard cmp command. This eliminates the need for manual decompression before comparison. If cmp is unavailable or reports an error (e.g., due to different file sizes or specific options not supported by cmp for the given scenario), gzcmp may fall back to using diff -q for a quicker check of differences, though its primary function aligns with cmp's byte-by-byte equality verification. It is a convenient tool for verifying the integrity or identity of compressed data without intermediate steps, often distributed as part of the gzip package.

Dependency: gzcmp relies on the cmp and potentially diff utilities being available in the system's PATH.
Performance: Comparing files with gzcmp might be slightly slower than comparing uncompressed files directly due to the overhead of on-the-fly decompression.
Error Clarity: Error messages and exit statuses primarily originate from the underlying cmp or diff commands, which might require familiarity with those tools for full interpretation.
No Specific Options: As a wrapper, gzcmp offers no unique options; all provided options are forwarded, which can sometimes be confusing if specific behavior is expected directly from gzcmp.

gzcmp typically returns the exit status of the underlying cmp command: 0 if the files are identical, 1 if they differ, and 2 if an error occurred (e.g., a file not found or an unreadable file).

When comparing .gz files, gzcmp uses pipes (e.g., gzip -cd file1.gz | cmp - file2 or gzip -cd file1.gz | gzip -cd file2.gz | cmp - -) to feed the decompressed content directly to cmp or diff without creating intermediate uncompressed files. This makes it efficient in terms of disk space usage.

gzcmp is a long-standing utility included as part of the GNU gzip compression software package, which first saw release in the early 1990s. Its primary purpose has always been to provide a convenient, transparent way to compare gzipped files, eliminating the manual steps of decompression. As a wrapper script, its core functionality and interface have remained consistent, reflecting its role as a simple helper utility for the gzip ecosystem.

cmp(1), diff(1), gzip(1), gzdiff(1), gzcat(1)