About listing bash options on `set`

Question

When we print the console settings with the echo $- command, we output himBHs by default. However, when we run the same command in any script file, we only output hB.

root@root:~# echo $-
himBHs
root@root:~# ./abc.sh 
hB
root@root:~#

What I'm wondering is, even though we're running the script from a /bin/bash environment, why don't the same default settings apply ?

For example, when I start a new sub-shell process with the command /bin/bash on the console and list the settings, I get output himBHs.

root@root:~# /bin/bash
root@root:~# echo $-
himBHs

When I try to perform the same process from within the shell file, the output I get is "hB".

root@root:~# ./abc.sh 
hB

I've tried the same process with shebang and without the shebang, but my script file is either bash script_file or ./script_file if I run, it gives the same result(hB).

What exactly am I missing?

Inian · Accepted Answer · 2020-01-28T08:04:21.323

5

Because when you run a script, the parent shell (the one you run your commands from) starts a non-interactive shell to run your script which has interactive flag disabled i and only turns on two options

-h to locate and remember (hash) commands as they are looked up for execution.
-B to allow the shell to perform brace expansion

You can see the complete list of set options which will be seen in the output of $- - The Set Builtin

Other options available in the interactive shell, -i to indicate to run the shell in interactive mode

-m to allow Job control
-H to enable ! style history substitution

edited Jan 28 '20 at 08:04

answered Jan 28 '20 at 07:53

Inian

12,807

1

Thank you your answer. Another issue I'm curious about is that we can assign ambient features with shebang. For example #!with /bin / bash-euxo, we can determine the properties of the environment in which the script file will be executed. However, the same operation'#!when we try /usr/bin / env bash-euxo, we get an error. Why? – testter Jan 28 '20 at 08:08
2

@testter: Yes, instead of adding duplicate information, you can look at these following posts Multiple arguments in shebang, Shebang line with #!/usr/bin/env command --argument fails on Linux and How to pass arguments to the shebang interpreter when executing a script? – Inian Jan 28 '20 at 08:11

score 4 · Answer 2 · answered Jan 28 '20 at 07:54

4

Several settings are enabled (or disabled) by default depending on whether the Bash is being run interactively, in POSIX mode, or other things. For example, from the output of help set:

  -H  Enable ! style history substitution.  This flag is on
      by default when the shell is interactive.

Or:

  -p  Turned on whenever the real and effective user ids do not match.

It just happens that for an interactive, non-POSIX-mode Bash, the options enabled are himBHs (-i is for interactive mode, -s is for reading in commands from standard input, the other options are listed in help set).

answered Jan 28 '20 at 07:54

muru

72,889

2

QuickQ: Why doesn't the GNU bash manual explain about the -s flag explicitly? or am I missing something here? – Inian Jan 28 '20 at 08:06
@Inian it's mentioned in Invoking Bash. If you're asking why it being listed in $- isn't explained, that's probably an oversight. It's only necessary to use it explicitiy for interactive shells if you have a non-option argument. – muru Jan 28 '20 at 08:48
1

You are wrong for -p. It needs to be set from outside to prevent the shell from resetting the effective uid/gid. – schily Jan 28 '20 at 11:52

About listing bash options on `set`

2 Answers2