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Bash attempts to write two shell prompts?
Can the empty spaces/background in a terminal be replaced with a random(but pretty) pattern of ASCII characters?How to write conditional if statement in bash shell script?Bash: show prompts if arguments weren't providedHow do I avoid echoing password (two simultaneous prompts)?bash: no job control in this shellBash shell script program that prompts for and reads two integers from the user.Find unused tty in the shell like bash?BASH question: using read, can I capture a single char OR arrow key (on keyup)
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I am looking at the strace output of a running bash process connected to
a terminal, for educational purposes.
My bash process has PID 2883.
I type
[OP@localhost ~]$ strace -e trace=openat,read,write,fork,vfork,clone,execve -p 2883 2> bash.strace
Into a terminal. I then go into my bash process, and have the following
interaction:
[OP@localhost ~]$ ls
Looking at the output, I see
strace: Process 2883 attached
read(0, "l", 1) = 1
write(2, "l", 1) = 1
read(0, "s", 1) = 1
write(2, "s", 1) = 1
read(0, "r", 1) = 1
write(2, "n", 1) = 1
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fec6b1d8e50) = 3917
--- SIGCHLD si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3917, si_uid=1000, si_status=0, si_utime=0, si_stime=0 ---
write(1, "33]0;OP@localhost:~7", 23) = 23
write(2, "[OP@localhost ~]$ ", 22) = 22
...
I am confused at the last two lines. It appears that bash is attempting
to write two shell prompts? What's going on here?
bash tty strace
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
add a comment
|
I am looking at the strace output of a running bash process connected to
a terminal, for educational purposes.
My bash process has PID 2883.
I type
[OP@localhost ~]$ strace -e trace=openat,read,write,fork,vfork,clone,execve -p 2883 2> bash.strace
Into a terminal. I then go into my bash process, and have the following
interaction:
[OP@localhost ~]$ ls
Looking at the output, I see
strace: Process 2883 attached
read(0, "l", 1) = 1
write(2, "l", 1) = 1
read(0, "s", 1) = 1
write(2, "s", 1) = 1
read(0, "r", 1) = 1
write(2, "n", 1) = 1
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fec6b1d8e50) = 3917
--- SIGCHLD si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3917, si_uid=1000, si_status=0, si_utime=0, si_stime=0 ---
write(1, "33]0;OP@localhost:~7", 23) = 23
write(2, "[OP@localhost ~]$ ", 22) = 22
...
I am confused at the last two lines. It appears that bash is attempting
to write two shell prompts? What's going on here?
bash tty strace
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
add a comment
|
I am looking at the strace output of a running bash process connected to
a terminal, for educational purposes.
My bash process has PID 2883.
I type
[OP@localhost ~]$ strace -e trace=openat,read,write,fork,vfork,clone,execve -p 2883 2> bash.strace
Into a terminal. I then go into my bash process, and have the following
interaction:
[OP@localhost ~]$ ls
Looking at the output, I see
strace: Process 2883 attached
read(0, "l", 1) = 1
write(2, "l", 1) = 1
read(0, "s", 1) = 1
write(2, "s", 1) = 1
read(0, "r", 1) = 1
write(2, "n", 1) = 1
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fec6b1d8e50) = 3917
--- SIGCHLD si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3917, si_uid=1000, si_status=0, si_utime=0, si_stime=0 ---
write(1, "33]0;OP@localhost:~7", 23) = 23
write(2, "[OP@localhost ~]$ ", 22) = 22
...
I am confused at the last two lines. It appears that bash is attempting
to write two shell prompts? What's going on here?
bash tty strace
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
I am looking at the strace output of a running bash process connected to
a terminal, for educational purposes.
My bash process has PID 2883.
I type
[OP@localhost ~]$ strace -e trace=openat,read,write,fork,vfork,clone,execve -p 2883 2> bash.strace
Into a terminal. I then go into my bash process, and have the following
interaction:
[OP@localhost ~]$ ls
Looking at the output, I see
strace: Process 2883 attached
read(0, "l", 1) = 1
write(2, "l", 1) = 1
read(0, "s", 1) = 1
write(2, "s", 1) = 1
read(0, "r", 1) = 1
write(2, "n", 1) = 1
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fec6b1d8e50) = 3917
--- SIGCHLD si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3917, si_uid=1000, si_status=0, si_utime=0, si_stime=0 ---
write(1, "33]0;OP@localhost:~7", 23) = 23
write(2, "[OP@localhost ~]$ ", 22) = 22
...
I am confused at the last two lines. It appears that bash is attempting
to write two shell prompts? What's going on here?
bash tty strace
bash tty strace
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
asked 8 hours ago
extremeaxe5extremeaxe5
4033 silver badges10 bronze badges
4033 silver badges10 bronze badges
add a comment
|
add a comment
|
1 Answer
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The <ESC>]0; sequence (shown as 33]0; by strace) is the escape sequence to set the terminal window title. It's terminated with the BEL character (7), so the first write sets the window title. The second prints the actual prompt. Note that even apart from the escape sequence, they're not exactly the same. The prompt has a surrounding [..] while the window title doesn't.
We can also see that the first write goes to stdout (fd 1, the first argument to write()), and the second to stderr. Bash prints the prompt to stderr, so the first write comes from somewhere else. That somewhere is probably PROMPT_COMMAND, like the one in Debian's default startup scripts for Bash. There's something like this in there:
case "$TERM" in
xterm*|rxvt*)
PROMPT_COMMAND='echo -ne "33]0;$USER@$HOSTNAME: $PWD07"'
;;
*)
;;
esac
It sets that PROMPT_COMMAND if running xterm or rxvt, which should support that escape sequence.
answered 7 hours ago
ilkkachuilkkachu
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1 Answer
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active
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The <ESC>]0; sequence (shown as 33]0; by strace) is the escape sequence to set the terminal window title. It's terminated with the BEL character (7), so the first write sets the window title. The second prints the actual prompt. Note that even apart from the escape sequence, they're not exactly the same. The prompt has a surrounding [..] while the window title doesn't.
We can also see that the first write goes to stdout (fd 1, the first argument to write()), and the second to stderr. Bash prints the prompt to stderr, so the first write comes from somewhere else. That somewhere is probably PROMPT_COMMAND, like the one in Debian's default startup scripts for Bash. There's something like this in there:
case "$TERM" in
xterm*|rxvt*)
PROMPT_COMMAND='echo -ne "33]0;$USER@$HOSTNAME: $PWD07"'
;;
*)
;;
esac
It sets that PROMPT_COMMAND if running xterm or rxvt, which should support that escape sequence.
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
add a comment
|
The <ESC>]0; sequence (shown as 33]0; by strace) is the escape sequence to set the terminal window title. It's terminated with the BEL character (7), so the first write sets the window title. The second prints the actual prompt. Note that even apart from the escape sequence, they're not exactly the same. The prompt has a surrounding [..] while the window title doesn't.
We can also see that the first write goes to stdout (fd 1, the first argument to write()), and the second to stderr. Bash prints the prompt to stderr, so the first write comes from somewhere else. That somewhere is probably PROMPT_COMMAND, like the one in Debian's default startup scripts for Bash. There's something like this in there:
case "$TERM" in
xterm*|rxvt*)
PROMPT_COMMAND='echo -ne "33]0;$USER@$HOSTNAME: $PWD07"'
;;
*)
;;
esac
It sets that PROMPT_COMMAND if running xterm or rxvt, which should support that escape sequence.
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
add a comment
|
The <ESC>]0; sequence (shown as 33]0; by strace) is the escape sequence to set the terminal window title. It's terminated with the BEL character (7), so the first write sets the window title. The second prints the actual prompt. Note that even apart from the escape sequence, they're not exactly the same. The prompt has a surrounding [..] while the window title doesn't.
We can also see that the first write goes to stdout (fd 1, the first argument to write()), and the second to stderr. Bash prints the prompt to stderr, so the first write comes from somewhere else. That somewhere is probably PROMPT_COMMAND, like the one in Debian's default startup scripts for Bash. There's something like this in there:
case "$TERM" in
xterm*|rxvt*)
PROMPT_COMMAND='echo -ne "33]0;$USER@$HOSTNAME: $PWD07"'
;;
*)
;;
esac
It sets that PROMPT_COMMAND if running xterm or rxvt, which should support that escape sequence.
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
The <ESC>]0; sequence (shown as 33]0; by strace) is the escape sequence to set the terminal window title. It's terminated with the BEL character (7), so the first write sets the window title. The second prints the actual prompt. Note that even apart from the escape sequence, they're not exactly the same. The prompt has a surrounding [..] while the window title doesn't.
We can also see that the first write goes to stdout (fd 1, the first argument to write()), and the second to stderr. Bash prints the prompt to stderr, so the first write comes from somewhere else. That somewhere is probably PROMPT_COMMAND, like the one in Debian's default startup scripts for Bash. There's something like this in there:
case "$TERM" in
xterm*|rxvt*)
PROMPT_COMMAND='echo -ne "33]0;$USER@$HOSTNAME: $PWD07"'
;;
*)
;;
esac
It sets that PROMPT_COMMAND if running xterm or rxvt, which should support that escape sequence.
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
answered 7 hours ago
ilkkachuilkkachu
68.8k10 gold badges113 silver badges198 bronze badges
68.8k10 gold badges113 silver badges198 bronze badges
add a comment
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add a comment
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