What is it “!!” and how it connected to `$_` or `$?`?
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I was playing with string substitution while learning a bit more of bash, and I have add !! into some dummy example echo $TEST/hey/!!...
I was surprised that !! was replaced with last entered command... what is it? is it somehow connected to magick codes link $? or $_ or even -. Is there anything else I can use in same manner in bash?
bash
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
add a comment |
I was playing with string substitution while learning a bit more of bash, and I have add !! into some dummy example echo $TEST/hey/!!...
I was surprised that !! was replaced with last entered command... what is it? is it somehow connected to magick codes link $? or $_ or even -. Is there anything else I can use in same manner in bash?
bash
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
5
Related (but doesn’t address the relationship with parameter expansion): Understanding the exclamation mark (!) in bash.
– Stephen Kitt
Dec 28 '18 at 9:46
2
They're not related, and they're not performed at the same stage (even if$_and!$will get you the same with simple commands).!will get you the "bang" / history expansion, a mechanism inherited fromcsh. Go read the "HISTORY EXPANSION" chapter from the bash manual.
– mosvy
Dec 28 '18 at 10:03
add a comment |
I was playing with string substitution while learning a bit more of bash, and I have add !! into some dummy example echo $TEST/hey/!!...
I was surprised that !! was replaced with last entered command... what is it? is it somehow connected to magick codes link $? or $_ or even -. Is there anything else I can use in same manner in bash?
bash
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
I was playing with string substitution while learning a bit more of bash, and I have add !! into some dummy example echo $TEST/hey/!!...
I was surprised that !! was replaced with last entered command... what is it? is it somehow connected to magick codes link $? or $_ or even -. Is there anything else I can use in same manner in bash?
bash
bash
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
asked Dec 28 '18 at 9:44
ButuzovButuzov
1113
1113
5
Related (but doesn’t address the relationship with parameter expansion): Understanding the exclamation mark (!) in bash.
– Stephen Kitt
Dec 28 '18 at 9:46
2
They're not related, and they're not performed at the same stage (even if$_and!$will get you the same with simple commands).!will get you the "bang" / history expansion, a mechanism inherited fromcsh. Go read the "HISTORY EXPANSION" chapter from the bash manual.
– mosvy
Dec 28 '18 at 10:03
add a comment |
5
Related (but doesn’t address the relationship with parameter expansion): Understanding the exclamation mark (!) in bash.
– Stephen Kitt
Dec 28 '18 at 9:46
2
They're not related, and they're not performed at the same stage (even if$_and!$will get you the same with simple commands).!will get you the "bang" / history expansion, a mechanism inherited fromcsh. Go read the "HISTORY EXPANSION" chapter from the bash manual.
– mosvy
Dec 28 '18 at 10:03
5
5
Related (but doesn’t address the relationship with parameter expansion): Understanding the exclamation mark (!) in bash.
– Stephen Kitt
Dec 28 '18 at 9:46
Related (but doesn’t address the relationship with parameter expansion): Understanding the exclamation mark (!) in bash.
– Stephen Kitt
Dec 28 '18 at 9:46
2
2
They're not related, and they're not performed at the same stage (even if
$_ and !$ will get you the same with simple commands). ! will get you the "bang" / history expansion, a mechanism inherited from csh. Go read the "HISTORY EXPANSION" chapter from the bash manual.– mosvy
Dec 28 '18 at 10:03
They're not related, and they're not performed at the same stage (even if
$_ and !$ will get you the same with simple commands). ! will get you the "bang" / history expansion, a mechanism inherited from csh. Go read the "HISTORY EXPANSION" chapter from the bash manual.– mosvy
Dec 28 '18 at 10:03
add a comment |
1 Answer
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votes
Bash performs different kinds of automatic replacements called expansions. For example, some of them are:
- History Expansion
- Path Expansion
- Parameter Expansion
- and others...
When you include !! bash automatically replaces by previous executed command. The character ! performs history expansion. For example !10 is replaced by the 10th command in the command history. $ does parameter and variable expansion. All of those characters: -, _, and ? are special parameter for bash.
The best source to learn about it is the bash manual: Bash Reference Manual: Top
The example you mention echo $TEST/hey/!! include both parameter and history expansions.
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
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oldest
votes
active
oldest
votes
Bash performs different kinds of automatic replacements called expansions. For example, some of them are:
- History Expansion
- Path Expansion
- Parameter Expansion
- and others...
When you include !! bash automatically replaces by previous executed command. The character ! performs history expansion. For example !10 is replaced by the 10th command in the command history. $ does parameter and variable expansion. All of those characters: -, _, and ? are special parameter for bash.
The best source to learn about it is the bash manual: Bash Reference Manual: Top
The example you mention echo $TEST/hey/!! include both parameter and history expansions.
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
add a comment |
Bash performs different kinds of automatic replacements called expansions. For example, some of them are:
- History Expansion
- Path Expansion
- Parameter Expansion
- and others...
When you include !! bash automatically replaces by previous executed command. The character ! performs history expansion. For example !10 is replaced by the 10th command in the command history. $ does parameter and variable expansion. All of those characters: -, _, and ? are special parameter for bash.
The best source to learn about it is the bash manual: Bash Reference Manual: Top
The example you mention echo $TEST/hey/!! include both parameter and history expansions.
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
add a comment |
Bash performs different kinds of automatic replacements called expansions. For example, some of them are:
- History Expansion
- Path Expansion
- Parameter Expansion
- and others...
When you include !! bash automatically replaces by previous executed command. The character ! performs history expansion. For example !10 is replaced by the 10th command in the command history. $ does parameter and variable expansion. All of those characters: -, _, and ? are special parameter for bash.
The best source to learn about it is the bash manual: Bash Reference Manual: Top
The example you mention echo $TEST/hey/!! include both parameter and history expansions.
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
Bash performs different kinds of automatic replacements called expansions. For example, some of them are:
- History Expansion
- Path Expansion
- Parameter Expansion
- and others...
When you include !! bash automatically replaces by previous executed command. The character ! performs history expansion. For example !10 is replaced by the 10th command in the command history. $ does parameter and variable expansion. All of those characters: -, _, and ? are special parameter for bash.
The best source to learn about it is the bash manual: Bash Reference Manual: Top
The example you mention echo $TEST/hey/!! include both parameter and history expansions.
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
answered Dec 28 '18 at 12:35
sebelksebelk
1,79611934
1,79611934
add a comment |
add a comment |
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5
Related (but doesn’t address the relationship with parameter expansion): Understanding the exclamation mark (!) in bash.
– Stephen Kitt
Dec 28 '18 at 9:46
2
They're not related, and they're not performed at the same stage (even if
$_and!$will get you the same with simple commands).!will get you the "bang" / history expansion, a mechanism inherited fromcsh. Go read the "HISTORY EXPANSION" chapter from the bash manual.– mosvy
Dec 28 '18 at 10:03