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Bash echo $-1 prints hb1. Why?

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1

If I ask bash to echo the -1th argument it prints hb1:

echo $-1
hb1

Why? What is it accessing?

bash arguments

share|improve this question

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  $- gets the current shell options (which is apparently "hb"). What did you expect it to do?
  
  – Gordon Davisson
  9 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I thought it might loop round like some arrays do. Thanks.
  
  – Neil
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Possible duplicate of Meaning of a hyphen as a special parameter?
  
  – muru
  9 hours ago
  

  
  
  
  

add a comment | 

1

If I ask bash to echo the -1th argument it prints hb1:

echo $-1
hb1

Why? What is it accessing?

bash arguments

share|improve this question

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  $- gets the current shell options (which is apparently "hb"). What did you expect it to do?
  
  – Gordon Davisson
  9 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I thought it might loop round like some arrays do. Thanks.
  
  – Neil
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Possible duplicate of Meaning of a hyphen as a special parameter?
  
  – muru
  9 hours ago
  

  
  
  
  

add a comment | 

If I ask bash to echo the -1th argument it prints hb1:

echo $-1
hb1

Why? What is it accessing?

bash arguments

share|improve this question

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

echo $-1
hb1

share|improve this question

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

share|improve this question

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

edited 6 hours ago

Jeff Schaller♦

47.1k1111 gold badges6868 silver badges153153 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

asked 9 hours ago

NeilNeil

10833 bronze badges

1 Answer
1

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10

You are not asking it to print the 1st argument, that would be: $1.

What you are asking for is a special parameter:

-

($-, a hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).

So your options are: hb

Then you see the 1 you've added is printed afterwards (hence hb1).

---

If you are looking to get the last argument (Not sure if that is what you meant by -1 argument), you can use Shell Parameter Expansion in the following form:

$ set -- one two three
$ echo "$@: -1"
three

share|improve this answer

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  $!# is also the value of the last parameter, using indirect expansion.
  
  – glenn jackman
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Hmmm: $@:~0 and eval echo $$# are also the last argument. :-)
  
  – Isaac
  8 hours ago
  

  
  
  
  

add a comment | 

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10

You are not asking it to print the 1st argument, that would be: $1.

What you are asking for is a special parameter:

-

($-, a hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).

So your options are: hb

Then you see the 1 you've added is printed afterwards (hence hb1).

---

If you are looking to get the last argument (Not sure if that is what you meant by -1 argument), you can use Shell Parameter Expansion in the following form:

$ set -- one two three
$ echo "$@: -1"
three

share|improve this answer

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  $!# is also the value of the last parameter, using indirect expansion.
  
  – glenn jackman
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Hmmm: $@:~0 and eval echo $$# are also the last argument. :-)
  
  – Isaac
  8 hours ago
  

  
  
  
  

add a comment | 

10

You are not asking it to print the 1st argument, that would be: $1.

What you are asking for is a special parameter:

-

($-, a hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).

So your options are: hb

Then you see the 1 you've added is printed afterwards (hence hb1).

---

If you are looking to get the last argument (Not sure if that is what you meant by -1 argument), you can use Shell Parameter Expansion in the following form:

$ set -- one two three
$ echo "$@: -1"
three

share|improve this answer

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  $!# is also the value of the last parameter, using indirect expansion.
  
  – glenn jackman
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Hmmm: $@:~0 and eval echo $$# are also the last argument. :-)
  
  – Isaac
  8 hours ago
  

  
  
  
  

add a comment | 

You are not asking it to print the 1st argument, that would be: $1.

What you are asking for is a special parameter:

-

($-, a hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).

So your options are: hb

Then you see the 1 you've added is printed afterwards (hence hb1).

---

If you are looking to get the last argument (Not sure if that is what you meant by -1 argument), you can use Shell Parameter Expansion in the following form:

$ set -- one two three
$ echo "$@: -1"
three

share|improve this answer

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges

$ set -- one two three
$ echo "$@: -1"
three

share|improve this answer

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges

answered 9 hours ago

Jesse_bJesse_b

17.1k33 gold badges4242 silver badges8484 bronze badges