我有一段脚本自己的mac机器默认用zsh，运行时一直很正常，今天给别的同事用，在bash下有些异常，追查了一下这个问题，把问题简化后如下：
#!/bin/bash
zsh -ic "which mvn"
zsh -ic "which mvn"
上面的脚本执行没有问题，但将里面的zsh换位bash，就会出现问题：
#!/bin/bash
bash -ic "which mvn"
bash -ic "which mvn"
在mac上执行，第一次bash -ic "which mvn"是成功的，但第二次执行时就会挂住：
➜ ./b.sh
/usr/local/bin/mvn
[1] + 24649 suspended (tty input) ./b.sh
/tmp/dd [23:43:21]
[jobs:1] ➜
后来想到which在zsh里是一个内置命令，而在bash下则是一个外部命令，可能有所差异，将zsh执行的命令也声明为外部命令：
#!/bin/bash
zsh -ic "/usr/bin/which mvn"
zsh -ic "/usr/bin/which mvn"
执行时会在第二次阻塞住，即使Ctrl-C也无法停止脚本。
这个问题很奇怪，两次以交互式调用shell执行一段命令（必须是外部命令）的话，第一次会成功，第二次则会suspend住。猜测可能是shell在第一次交互式执行结束后改变了上下文的什么状态，导致第二次再执行的时候挂住。在linux上用strace跟踪了一下脚本，看样子是因为SIGTTIN信号量所致，但其中缘由并不清楚，我把代码和strace的信息贴在这里，希望明白的人解释一下
$ cat b.sh
#!/bin/bash
bash -ic "ls"
bash -ic "ls"
$ strace ./b.sh
[hongjiang@localhost dd]$ strace ./b.sh
execve("./b.sh", ["./b.sh"], [/* 31 vars */]) = 0
brk(0) = 0x1175000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa545ddf000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=32094, ...}) = 0
mmap(NULL, 32094, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa545dd7000
close(3) = 0
open("/lib64/libtinfo.so.5", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@\316\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=174520, ...}) = 0
mmap(NULL, 2268928, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa545995000
mprotect(0x7fa5459ba000, 2097152, PROT_NONE) = 0
mmap(0x7fa545bba000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x25000) = 0x7fa545bba000
close(3) = 0
open("/lib64/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\16\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=19512, ...}) = 0
mmap(NULL, 2109744, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa545791000
mprotect(0x7fa545794000, 2093056, PROT_NONE) = 0
mmap(0x7fa545993000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fa545993000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\34\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2107760, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa545dd6000
mmap(NULL, 3932736, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa5453d0000
mprotect(0x7fa545586000, 2097152, PROT_NONE) = 0
mmap(0x7fa545786000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b6000) = 0x7fa545786000
mmap(0x7fa54578c000, 16960, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa54578c000
close(3) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa545dd4000
arch_prctl(ARCH_SET_FS, 0x7fa545dd4740) = 0
mprotect(0x7fa545786000, 16384, PROT_READ) = 0
mprotect(0x7fa545993000, 4096, PROT_READ) = 0
mprotect(0x7fa545bba000, 16384, PROT_READ) = 0
mprotect(0x6dc000, 4096, PROT_READ) = 0
mprotect(0x7fa545de0000, 4096, PROT_READ) = 0
munmap(0x7fa545dd7000, 32094) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
open("/dev/tty", O_RDWR|O_NONBLOCK) = 3
close(3) = 0
brk(0) = 0x1175000
brk(0x1196000) = 0x1196000
brk(0) = 0x1196000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=106065056, ...}) = 0
mmap(NULL, 106065056, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa53eea9000
close(3) = 0
brk(0) = 0x1196000
getuid() = 1000
getgid() = 1000
geteuid() = 1000
getegid() = 1000
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
open("/proc/meminfo", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa545dde000
read(3, "MemTotal: 1017160 kB\nMemF"..., 1024) = 1024
close(3) = 0
munmap(0x7fa545dde000, 4096) = 0
rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTORER|SA_RESTART, 0x7fa545405650}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTORER|SA_RESTART, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER|SA_RESTART, 0x7fa545405650}, 8) = 0
rt_sigaction(SIGINT, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGINT, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, 8) = 0
rt_sigaction(SIGQUIT, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGQUIT, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigaction(SIGQUIT, {SIG_IGN, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, 8) = 0
uname({sys="Linux", node="localhost.localdomain", ...}) = 0
stat("/tmp/dd", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
stat(".", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
getpid() = 2945
open("/usr/lib64/gconv/gconv-modules.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=26254, ...}) = 0
mmap(NULL, 26254, PROT_READ, MAP_SHARED, 3, 0) = 0x7fa545dd8000
close(3) = 0
getppid() = 2942
getpgrp() = 2942
rt_sigaction(SIGCHLD, {0x441090, [], SA_RESTORER|SA_RESTART, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER|SA_RESTART, 0x7fa545405650}, 8) = 0
getrlimit(RLIMIT_NPROC, {rlim_cur=3909, rlim_max=3909}) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
open("./b.sh", O_RDONLY) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 0x7fff54edec40) = -1 ENOTTY (Inappropriate ioctl for device)
lseek(3, 0, SEEK_CUR) = 0
read(3, "#!/bin/sh\n\nbash -ic \"ls\"\nbash -i"..., 80) = 39
lseek(3, 0, SEEK_SET) = 0
getrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=4*1024}) = 0
fcntl(255, F_GETFD) = -1 EBADF (Bad file descriptor)
dup2(3, 255) = 255
close(3) = 0
fcntl(255, F_SETFD, FD_CLOEXEC) = 0
fcntl(255, F_GETFL) = 0x8000 (flags O_RDONLY|O_LARGEFILE)
fstat(255, {st_mode=S_IFREG|0775, st_size=39, ...}) = 0
lseek(255, 0, SEEK_CUR) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
read(255, "#!/bin/sh\n\nbash -ic \"ls\"\nbash -i"..., 39) = 39
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
stat(".", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
stat("/home/hongjiang/.local/bin/bash", 0x7fff54ede900) = -1 ENOENT (No such file or directory)
stat("/home/hongjiang/bin/bash", 0x7fff54ede900) = -1 ENOENT (No such file or directory)
stat("/data/program/scala/bin/bash", 0x7fff54ede900) = -1 ENOENT (No such file or directory)
stat("/usr/lib64/qt-3.3/bin/bash", 0x7fff54ede900) = -1 ENOENT (No such file or directory)
stat("/usr/local/bin/bash", 0x7fff54ede900) = -1 ENOENT (No such file or directory)
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
geteuid() = 1000
getegid() = 1000
getuid() = 1000
getgid() = 1000
access("/usr/bin/bash", X_OK) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
geteuid() = 1000
getegid() = 1000
getuid() = 1000
getgid() = 1000
access("/usr/bin/bash", R_OK) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
geteuid() = 1000
getegid() = 1000
getuid() = 1000
getgid() = 1000
access("/usr/bin/bash", X_OK) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
geteuid() = 1000
getegid() = 1000
getuid() = 1000
getgid() = 1000
access("/usr/bin/bash", R_OK) = 0
rt_sigprocmask(SIG_BLOCK, [INT CHLD], [], 8) = 0
lseek(255, -14, SEEK_CUR) = 25
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fa545dd4a10) = 2946
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGINT, {0x43e500, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, 8) = 0
wait4(-1, b.sh
[{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 2946
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2946, si_status=0, si_utime=0, si_stime=0} ---
wait4(-1, 0x7fff54ede450, WNOHANG, NULL) = -1 ECHILD (No child processes)
rt_sigreturn() = 0
rt_sigaction(SIGINT, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, {0x43e500, [], SA_RESTORER, 0x7fa545405650}, 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
read(255, "bash -ic \"ls\"\n", 39) = 14
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
geteuid() = 1000
getegid() = 1000
getuid() = 1000
getgid() = 1000
access("/usr/bin/bash", X_OK) = 0
stat("/usr/bin/bash", {st_mode=S_IFREG|0755, st_size=960384, ...}) = 0
geteuid() = 1000
getegid() = 1000
getuid() = 1000
getgid() = 1000
access("/usr/bin/bash", R_OK) = 0
rt_sigprocmask(SIG_BLOCK, [INT CHLD], [], 8) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fa545dd4a10) = 2967
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGINT, {0x43e500, [], SA_RESTORER, 0x7fa545405650}, {SIG_DFL, [], SA_RESTORER, 0x7fa545405650}, 8) = 0
wait4(-1, 0x7fff54edea00, 0, NULL) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGTTIN {si_signo=SIGTTIN, si_code=SI_USER, si_pid=2967, si_uid=1000} ---
--- stopped by SIGTTIN ---
首先，解决这个问题的方法是使用`bash -lc`。
另外，我奇怪的是`bash -ic “ls”`的语义应该是先执行命令`ls`，再进入bash的交互模式，为什么实际上第一次直接没有进入交互模式就退出了。`python -ic “print 1″`就是这种语义。
-i选项优先被执行，shell会以交互式加载用户配置文件之后再执行后续的命令：
➜ zsh -c “which mvn”
/usr/local/bin/mvn
➜ zsh -ic “which mvn”
mvn: aliased to mvn -s /data/tools/maven/settings-wc.xml
/usr/local/bin/mvn
发现`bash -ic “which mvn”; python -ic “print 1″`在脚本中执行也会在`bash -ic “which mvn”`之后发出SIGTTIN
脚本里要用交互式 “bash -i” ，文章里写成非交互式，笔误已经更新。
应该是 -i 选项在 bash 和 zsh 的处理方式是不同的原因造成的，有什么需求需要加上 -i 选项吗？
用交互式的原因是想要更准确的找到用户在那个shell下的命令是不是有被alias过，假设用户mvn命令有2个，除了默认PATH 下 “/usr/local/bin/mvn”，还有一个 “/some_dir/mvn”，而如果用户在自己的.bashrc里 alias mvn=’/some_path/mvn’ ，我希望得到用户alias过的命令，所以指定-i，确保shell会执行用户配置文件。
https://hackintoshrao.com/2012/08/08/singals-in-gnulinux-sigcont-sigttin-and-sigttou/
#!/bin/bash
zsh -ic “/usr/bin/which mvn” && stty tostop
zsh -ic “/usr/bin/which mvn”
起码可以看到类似这样的输出：
[1] + 89139 suspended (tty output) ./1.sh