ฉันคิดว่า (วิธีดั้งเดิม) โดยใช้ท่อนั้นเร็วกว่าเล็กน้อย ในกล่องของฉันฉันใช้straceคำสั่งเพื่อดูว่าเกิดอะไรขึ้น:
ไม่มีท่อ:
toc@UnixServer:~$ strace wc -l < wrong_output.c
execve("/usr/bin/wc", ["wc", "-l"], [/* 18 vars */]) = 0
brk(0) = 0x8b50000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb77ad000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=29107, ...}) = 0
mmap2(NULL, 29107, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb77a5000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0p\222\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1552584, ...}) = 0
mmap2(NULL, 1563160, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7627000
mmap2(0xb779f000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x178) = 0xb779f000
mmap2(0xb77a2000, 10776, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb77a2000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7626000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb76268d0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb779f000, 8192, PROT_READ) = 0
mprotect(0x804f000, 4096, PROT_READ) = 0
mprotect(0xb77ce000, 4096, PROT_READ) = 0
munmap(0xb77a5000, 29107) = 0
brk(0) = 0x8b50000
brk(0x8b71000) = 0x8b71000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=5540198, ...}) = 0
mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7426000
mmap2(NULL, 1507328, PROT_READ, MAP_PRIVATE, 3, 0x2a8) = 0xb72b6000
close(3) = 0
open("/usr/share/locale/locale.alias", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb77ac000
read(3, "# Locale name alias data base.\n#"..., 4096) = 2570
read(3, "", 4096) = 0
close(3) = 0
munmap(0xb77ac000, 4096) = 0
open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/fr_FR/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/fr.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/fr/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/fr_FR.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/fr_FR.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/fr_FR/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/fr.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/fr.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/fr/LC_MESSAGES/coreutils.mo", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=316721, ...}) = 0
mmap2(NULL, 316721, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7268000
close(3) = 0
open("/usr/lib/i386-linux-gnu/gconv/gconv-modules.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=26064, ...}) = 0
mmap2(NULL, 26064, PROT_READ, MAP_SHARED, 3, 0) = 0xb7261000
close(3) = 0
read(0, "#include<stdio.h>\n\nint main(int "..., 16384) = 180
read(0, "", 16384) = 0
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7260000
write(1, "13\n", 313
) = 3
close(0) = 0
close(1) = 0
munmap(0xb7260000, 4096) = 0
close(2) = 0
exit_group(0) = ?
และท่อ:
toc@UnixServer:~$ strace cat wrong_output.c | wc -l
execve("/bin/cat", ["cat", "wrong_output.c"], [/* 18 vars */]) = 0
brk(0) = 0xa017000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb774b000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=29107, ...}) = 0
mmap2(NULL, 29107, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7743000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0p\222\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1552584, ...}) = 0
mmap2(NULL, 1563160, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb75c5000
mmap2(0xb773d000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x178) = 0xb773d000
mmap2(0xb7740000, 10776, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7740000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb75c4000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb75c48d0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb773d000, 8192, PROT_READ) = 0
mprotect(0x8051000, 4096, PROT_READ) = 0
mprotect(0xb776c000, 4096, PROT_READ) = 0
munmap(0xb7743000, 29107) = 0
brk(0) = 0xa017000
brk(0xa038000) = 0xa038000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=5540198, ...}) = 0
mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb73c4000
mmap2(NULL, 1507328, PROT_READ, MAP_PRIVATE, 3, 0x2a8) = 0xb7254000
close(3) = 0
fstat64(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
open("wrong_output.c", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0664, st_size=180, ...}) = 0
read(3, "#include<stdio.h>\n\nint main(int "..., 32768) = 180
write(1, "#include<stdio.h>\n\nint main(int "..., 180) = 180
read(3, "", 32768) = 0
close(3) = 0
close(1) = 0
close(2) = 0
exit_group(0) = ?
13
คุณสามารถทำการทดสอบstraceและtimeสั่งการด้วยคำสั่งที่มากขึ้นและยาวขึ้นเพื่อการเปรียบเทียบที่ดี
catเป็นท่อตัวตน เพียงสตรีมอินพุตไปยังเอาต์พุตเท่านั้น หากโปรแกรมที่สองในห่วงโซ่สามารถรับอินพุตจากอาร์กิวเมนต์เดียวกันกับที่คุณส่งผ่านไปcat(หรือจากอินพุตมาตรฐานหากคุณไม่ส่งอาร์กิวเมนต์) ก็catจะไม่มีประโยชน์อย่างยิ่งและส่งผลให้มีการแยกกระบวนการเพิ่มเติมและมีท่อเพิ่มเติมเท่านั้น สร้างขึ้น