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GeezerVison is showing github.com — cmp: size the -l offset column from the regular-file operand when the other is stdin by sarankumar1325 · Pull Request #373 · uutils/diffutils

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@sarankumar1325

@sarankumar1325 sarankumar1325 commented Nov 10, 2026

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Fixes #348.

cmp -l sizes the offset column from the smallest number of bytes that can still be compared. #330 did this only when both operands could be stat'ed as paths. With standard input on one side (cat c1 | cmp -l - c2), the width stayed at the u64::MAX width (19 columns).

This change adds a regular_file_size() helper that returns the size only for operands that are regular files (not -, pipes or devices). The offset width is now narrowed by the size, minus the skip, of each regular-file operand. GNU cmp does the same. The -s early exit for files of different sizes still needs both sizes, and it now uses only regular-file sizes (a device's len() of 0 is no longer treated as a real size).

$ printf 'abcdefghij' > c1; printf 'abcdeXghiY' > c2
$ cat c1 | diffutils cmp -l - c2
 6 146 130
10 152 131

Test: cmp_verbose_offset_width_stdin (from the issue, plus the reversed operand order). It fails on main with the 19-column output and passes with this change. cargo test --test tests, cargo fmt and cargo clippy -- -D warnings are clean. The ed_diff permutation unit tests can't run locally because ed isn't installed on my machine.

I used an AI assistant to help with this change. I reviewed and tested it myself.

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@sarankumar1325
cmp: size the -l offset column from the regular-file operand when the…
8fd5107 
… other is stdin

The offset width was only narrowed when both operands could be stat'ed,
so 'cmp -l - file' used the 19-column u64::MAX width. Like GNU cmp, use
the size of every operand that is a regular file (minus its skip) and
ignore standard input, pipes and devices.

Fixes uutils#348
Copilot AI balanced review requested due to automatic review settings November 10, 2026 21:32
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sylvestre
sylvestre reviewed Nov 10, 2026
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Comment thread src/cmp.rs Outdated
}

#[cfg(not(target_os = "windows"))]
let size = meta.len();

@sylvestre sylvestre Nov 10, 2026

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meta.len() works on windows too, do we still need the cfg here?

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@sarankumar1325
cmp: use Metadata::len on every platform for regular_file_size
d1867e7 
Metadata::len() is cross-platform, so the Windows-only file_size() branch
and its MetadataExt import are not needed.
Copilot AI balanced review requested due to automatic review settings November 10, 2026 22:26
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sylvestre
sylvestre reviewed Nov 11, 2026
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Comment thread src/cmp.rs
// been asked to show even the first difference, we can quit early.
// If the files have different sizes, we already know they are not identical. If we have not
// been asked to show even the first difference, we can quit early.
if let (Some(a_size), Some(b_size)) = (a_size, b_size) {

@sylvestre sylvestre Nov 11, 2026

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this also changes -s with a pipe/device on one side, could you please add a test for it?

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@sarankumar1325
cmp: test -s with a pipe or device operand
7a2021f 
/dev/stdin as a pipe and /dev/null as a character device now skip the
size-based -s early exit and are compared by content, on either side.

Signed-off-by: sarankumar1325 <[email protected]>
Copilot AI balanced review requested due to automatic review settings November 11, 2026 13:52
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@sarankumar1325
cmp: rustfmt the -s pipe test
3a46b4a 
Signed-off-by: sarankumar1325 <[email protected]>
Copilot AI balanced review requested due to automatic review settings November 11, 2026 13:52
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cmp - -l offset column is 19 characters wide when one operand is stdin

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@sarankumar1325 @sylvestre
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