管道緩衝區有多大？
作為評論，我很困惑為什麼makefile中的“| true”與“|| true”使用者cjm寫道：
另一個需要避免的原因
| true是，如果該命令產生了足夠的輸出來填滿管道緩衝區，它將阻塞等待 true 來讀取它。我們有什麼方法可以找出管道緩衝區的大小嗎？
管道緩衝區的容量因係統而異（甚至在同一系統上也可能不同）。我不確定是否有一種快速、簡單且跨平台的方法來查找管道的容量。
例如，Mac OS X 預設使用 16384 字節的容量，但如果對管道進行大量寫入，則可以切換到 65336 字節的容量，或者如果已經有太多核心記憶體，則會切換到單個系統頁面的容量被管道緩衝區使用（參見
xnu/bsd/sys/pipe.h, 和xnu/bsd/kern/sys_pipe.c; 因為這些來自 FreeBSD，同樣的行為也可能發生在那裡）。一個 Linux *pipe(7)*手冊頁說，自 Linux 2.6.11 以來管道容量為 65536 字節，而在此之前的單個系統頁面（例如（32 位）x86 系統上的 4096 字節）。程式碼（
include/linux/pipe_fs_i.h和fs/pipe.c）似乎使用了 16 個系統頁面（即，如果系統頁面為 4 KiB，則為 64 KiB），但每個管道的緩衝區可以通過管道上的fcntl進行調整（最大容量預設為 1048576字節，但可以通過/proc/sys/fs/pipe-max-size)) 更改。這是我用來測試系統上的管道容量的一個小bash / perl組合：
#!/bin/bash test $# -ge 1 || { echo "usage: $0 write-size [wait-time]"; exit 1; } test $# -ge 2 || set -- "$@" 1 bytes_written=$( { exec 3>&1 { perl -e ' $size = $ARGV[0]; $block = q(a) x $size; $num_written = 0; sub report { print STDERR $num_written * $size, qq(\n); } report; while (defined syswrite STDOUT, $block) { $num_written++; report; } ' "$1" 2>&3 } | (sleep "$2"; exec 0<&-); } | tail -1 ) printf "write size: %10d; bytes successfully before error: %d\n" \ "$1" "$bytes_written"這是我發現在 Mac OS X 10.6.7 系統上以各種寫入大小執行它的結果（請注意大於 16KiB 的寫入更改）：
% /bin/bash -c 'for p in {0..18}; do /tmp/ts.sh $((2 ** $p)) 0.5; done' write size: 1; bytes successfully before error: 16384 write size: 2; bytes successfully before error: 16384 write size: 4; bytes successfully before error: 16384 write size: 8; bytes successfully before error: 16384 write size: 16; bytes successfully before error: 16384 write size: 32; bytes successfully before error: 16384 write size: 64; bytes successfully before error: 16384 write size: 128; bytes successfully before error: 16384 write size: 256; bytes successfully before error: 16384 write size: 512; bytes successfully before error: 16384 write size: 1024; bytes successfully before error: 16384 write size: 2048; bytes successfully before error: 16384 write size: 4096; bytes successfully before error: 16384 write size: 8192; bytes successfully before error: 16384 write size: 16384; bytes successfully before error: 16384 write size: 32768; bytes successfully before error: 65536 write size: 65536; bytes successfully before error: 65536 write size: 131072; bytes successfully before error: 0 write size: 262144; bytes successfully before error: 0Linux 3.19 上的相同腳本：
/bin/bash -c 'for p in {0..18}; do /tmp/ts.sh $((2 ** $p)) 0.5; done' write size: 1; bytes successfully before error: 65536 write size: 2; bytes successfully before error: 65536 write size: 4; bytes successfully before error: 65536 write size: 8; bytes successfully before error: 65536 write size: 16; bytes successfully before error: 65536 write size: 32; bytes successfully before error: 65536 write size: 64; bytes successfully before error: 65536 write size: 128; bytes successfully before error: 65536 write size: 256; bytes successfully before error: 65536 write size: 512; bytes successfully before error: 65536 write size: 1024; bytes successfully before error: 65536 write size: 2048; bytes successfully before error: 65536 write size: 4096; bytes successfully before error: 65536 write size: 8192; bytes successfully before error: 65536 write size: 16384; bytes successfully before error: 65536 write size: 32768; bytes successfully before error: 65536 write size: 65536; bytes successfully before error: 65536 write size: 131072; bytes successfully before error: 0 write size: 262144; bytes successfully before error: 0注意：
PIPE_BUF在 C 標頭檔中定義的值（以及 的pathconf值_PC_PIPE_BUF）沒有指定管道的容量，而是可以原子寫入的最大字節數（參見POSIX write(2)）。/* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual memory allocation, whereas PIPE_BUF makes atomicity guarantees. */