Meaning of BASH operators “^â€, “|†and “$†in condition ^(n|N)$
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In my script, I am trying to make "Try again? [y/N]" condition...
if [[ "$response" =~ ^(n|no)$ ]]; then do something...,
but I don't understand meaning of symbols "^" and "$" used here. I tried just simple [[ if $response =~ (n|no) ]] and it worked, but if I typed something like "nein" it still worked... I took pipe (|) as "OR" operator, but it's probably also wrong.
Could somebody explain me the meaning of whole condition? It works, but I would like to know meaning too... Thank you very much.
bash
edited Mar 24 at 23:44
Jesse_b
10.4k22658
asked Mar 24 at 23:43
Michal
141
add a comment |Â
up vote
2
down vote
favorite
In my script, I am trying to make "Try again? [y/N]" condition...
if [[ "$response" =~ ^(n|no)$ ]]; then do something...,
but I don't understand meaning of symbols "^" and "$" used here. I tried just simple [[ if $response =~ (n|no) ]] and it worked, but if I typed something like "nein" it still worked... I took pipe (|) as "OR" operator, but it's probably also wrong.
Could somebody explain me the meaning of whole condition? It works, but I would like to know meaning too... Thank you very much.
bash
edited Mar 24 at 23:44
Jesse_b
10.4k22658
asked Mar 24 at 23:43
Michal
141
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
In my script, I am trying to make "Try again? [y/N]" condition...
if [[ "$response" =~ ^(n|no)$ ]]; then do something...,
but I don't understand meaning of symbols "^" and "$" used here. I tried just simple [[ if $response =~ (n|no) ]] and it worked, but if I typed something like "nein" it still worked... I took pipe (|) as "OR" operator, but it's probably also wrong.
Could somebody explain me the meaning of whole condition? It works, but I would like to know meaning too... Thank you very much.
bash
edited Mar 24 at 23:44
Jesse_b
10.4k22658
asked Mar 24 at 23:43
Michal
141
In my script, I am trying to make "Try again? [y/N]" condition...
if [[ "$response" =~ ^(n|no)$ ]]; then do something...,
but I don't understand meaning of symbols "^" and "$" used here. I tried just simple [[ if $response =~ (n|no) ]] and it worked, but if I typed something like "nein" it still worked... I took pipe (|) as "OR" operator, but it's probably also wrong.
Could somebody explain me the meaning of whole condition? It works, but I would like to know meaning too... Thank you very much.
bash
edited Mar 24 at 23:44
Jesse_b
10.4k22658
asked Mar 24 at 23:43
Michal
141
edited Mar 24 at 23:44
Jesse_b
10.4k22658
edited Mar 24 at 23:44
Jesse_b
10.4k22658
edited Mar 24 at 23:44
Jesse_b
10.4k22658
10.4k22658
asked Mar 24 at 23:43
Michal
141
asked Mar 24 at 23:43
Michal
141
asked Mar 24 at 23:43
Michal
141
141
add a comment |Â
add a comment |Â
1 Answer
1
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oldest
votes
up vote
8
down vote
These are regular expression special characters.
^ is an anchor for the start of string (So nothing can be before the match)
$ is an anchor for the end of string (so nothing can be after the match)
| is OR as you suspected
The =~ tells the bash extended test that the string on the right is an extended regular expression and will exit with 0 for match and 1 for anything else.
[[ if $response =~ (n|no) ]] is flawed as the if should be outside the brackets, but assuming that is a typo in your question it will succeed if response contains an n at all. You likely want the start and end anchors so that only n or no will match.
answered Mar 24 at 23:46
Jesse_b
10.4k22658
3
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
8
down vote
These are regular expression special characters.
^ is an anchor for the start of string (So nothing can be before the match)
$ is an anchor for the end of string (so nothing can be after the match)
| is OR as you suspected
The =~ tells the bash extended test that the string on the right is an extended regular expression and will exit with 0 for match and 1 for anything else.
[[ if $response =~ (n|no) ]] is flawed as the if should be outside the brackets, but assuming that is a typo in your question it will succeed if response contains an n at all. You likely want the start and end anchors so that only n or no will match.
answered Mar 24 at 23:46
Jesse_b
10.4k22658
3
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
add a comment |Â
up vote
8
down vote
These are regular expression special characters.
^ is an anchor for the start of string (So nothing can be before the match)
$ is an anchor for the end of string (so nothing can be after the match)
| is OR as you suspected
The =~ tells the bash extended test that the string on the right is an extended regular expression and will exit with 0 for match and 1 for anything else.
[[ if $response =~ (n|no) ]] is flawed as the if should be outside the brackets, but assuming that is a typo in your question it will succeed if response contains an n at all. You likely want the start and end anchors so that only n or no will match.
answered Mar 24 at 23:46
Jesse_b
10.4k22658
3
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
add a comment |Â
up vote
8
down vote
up vote
8
down vote
These are regular expression special characters.
^ is an anchor for the start of string (So nothing can be before the match)
$ is an anchor for the end of string (so nothing can be after the match)
| is OR as you suspected
The =~ tells the bash extended test that the string on the right is an extended regular expression and will exit with 0 for match and 1 for anything else.
[[ if $response =~ (n|no) ]] is flawed as the if should be outside the brackets, but assuming that is a typo in your question it will succeed if response contains an n at all. You likely want the start and end anchors so that only n or no will match.
answered Mar 24 at 23:46
Jesse_b
10.4k22658
These are regular expression special characters.
^ is an anchor for the start of string (So nothing can be before the match)
$ is an anchor for the end of string (so nothing can be after the match)
| is OR as you suspected
The =~ tells the bash extended test that the string on the right is an extended regular expression and will exit with 0 for match and 1 for anything else.
[[ if $response =~ (n|no) ]] is flawed as the if should be outside the brackets, but assuming that is a typo in your question it will succeed if response contains an n at all. You likely want the start and end anchors so that only n or no will match.
answered Mar 24 at 23:46
Jesse_b
10.4k22658
edited Mar 25 at 11:03
answered Mar 24 at 23:46
Jesse_b
10.4k22658
answered Mar 24 at 23:46
Jesse_b
10.4k22658
answered Mar 24 at 23:46
Jesse_b
10.4k22658
10.4k22658
3
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
add a comment |Â
3
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
3
3
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
Probably also worth mentioning that =~ is what causes the right hand side to be interpreted as a regex which causes ‘nein’ to make the test true.
– neal
Mar 25 at 4:52
add a comment |Â
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