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Using regular expressions in “less”

Announcing the arrival of Valued Associate #679: Cesar Manara

Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)

2019 Community Moderator Election Results

Why I closed the “Why is Kali so hard” questionUsing regular expressions with cpVIM see regular expressions matches as you typeMatch multiple regular expressions from a single file using awkCan I force `man` to do lower case sensitive matching?Regular expressions in a shellUltraEdit - regular expressions replacementHow do I search bash's history in vi mode for “foo.*bar”Extended Regular Expressions (EREs): How do I include pattern but exclude specific superset of pattern in matches?How does storing the regular expression in a shell variable avoid problems with quoting characters that are special to the shell?How to indicate start of line in less search of man pages?

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I'm trying to use a regular expression in the man page of Bash by using less.

I press / in less to enter a pattern, and I type z and press the Enter. I expected it to not match upper-case z (Z), but it does.

How do I make it not match Z? What kind of regular expressions are these that are not case sensitive?

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

asked Apr 10 at 18:42

regex

223

New contributor

add a comment |

I'm trying to use a regular expression in the man page of Bash by using less.

I press / in less to enter a pattern, and I type z and press the Enter. I expected it to not match upper-case z (Z), but it does.

How do I make it not match Z? What kind of regular expressions are these that are not case sensitive?

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

asked Apr 10 at 18:42

regex

223

New contributor

add a comment |

I'm trying to use a regular expression in the man page of Bash by using less.

I press / in less to enter a pattern, and I type z and press the Enter. I expected it to not match upper-case z (Z), but it does.

How do I make it not match Z? What kind of regular expressions are these that are not case sensitive?

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

asked Apr 10 at 18:42

regex

223

New contributor

I'm trying to use a regular expression in the man page of Bash by using less.

I press / in less to enter a pattern, and I type z and press the Enter. I expected it to not match upper-case z (Z), but it does.

How do I make it not match Z? What kind of regular expressions are these that are not case sensitive?

regular-expression less case-sensitivity

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

asked Apr 10 at 18:42

regex

223

New contributor

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

asked Apr 10 at 18:42

regex

223

New contributor

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

edited Apr 11 at 16:39

Kusalananda♦

142k18264440

asked Apr 10 at 18:42

regex

223

New contributor

asked Apr 10 at 18:42

regex

223

asked Apr 10 at 18:42

regex

223

New contributor

regex is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment |

2 Answers
2

active

oldest

votes

It's explained in the man page for less.

The default action for REs is to ignore case if there are no uppercase characters present, but to act case-sensitively otherwise.

There are three modes available within less:

Case context dependent: a search or RE without uppercase characters is considered to be case-insensitive, but a search or RE containing at least one uppercase character is considered to be case-sensitive. Examples: abc will match abc and aBC, but aBc will only match aBc and not abc or ABC. This is the default setting.

Case sensitive: a search or RE pays full regard to the case of any letter. Example: abC will match only abC and not abc or ABC.

Case insensitive: a search or RE pays no regard to the case of any letter. Example: abC will match any of abc, abC, or ABC.

You can toggle case sensitive comparisons with -I, and case context sensitive comparisons with -i.

The control can be specified in three ways:

On the command line, for example less -I bigfile.txt.

In the environment, for example export LESS=-i and later less bigfile.txt.

Within less itself, for example by starting less bigfile.txt and then typing -i.

edited Apr 11 at 16:21

answered Apr 10 at 18:53

roaima

46.2k758124

Hey, roaima. I think this is incorrect. ``` -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains uppercase letters, then that search does not ignore case. -I or --IGNORE-CASE Like -i, but searches ignore case even if the pattern contains uppercase letters. ``` From my experiments, it behaves as -I, not as -i.

– regex
Apr 10 at 23:14

1

You could also append |$A (which translates as or A after the end of the line) for your pattern to become case sensitive without having to the change the settings.

– Stéphane Chazelas
Apr 11 at 16:35

@StéphaneChazelas that's thrown me. I had thought $ was only special at the end of an RE (or RE clause), so $A would match a dollar and a capital letter, but A$ would match a capital at the end of a line. (Update: I can't even mimic this with perl, but definitely works with less.)

– roaima
Apr 11 at 16:50

@roaima, it's different between BRE and ERE, POSIX requires BRE $a to match on $a, and ERE $a to not match ($ to match the end of the subject wherever it's found). In Perl/PCRE, $ matches at the end of the subject or before a trailing line delimiter at the end of the subject, or if the m flag is enabled ((?m)) at the end of the subject or before any line delimiter in the subject.

– Stéphane Chazelas
Apr 11 at 17:26

add a comment |

Pretty sure you can get around that by using -i or +i in order to set less to default.

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

answered Apr 10 at 18:49

6d6d

212

New contributor

Thank you, 6b6b.

– regex
Apr 10 at 18:59

add a comment |

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2 Answers
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2 Answers
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It's explained in the man page for less.

The default action for REs is to ignore case if there are no uppercase characters present, but to act case-sensitively otherwise.

There are three modes available within less:

Case context dependent: a search or RE without uppercase characters is considered to be case-insensitive, but a search or RE containing at least one uppercase character is considered to be case-sensitive. Examples: abc will match abc and aBC, but aBc will only match aBc and not abc or ABC. This is the default setting.

Case sensitive: a search or RE pays full regard to the case of any letter. Example: abC will match only abC and not abc or ABC.

Case insensitive: a search or RE pays no regard to the case of any letter. Example: abC will match any of abc, abC, or ABC.

You can toggle case sensitive comparisons with -I, and case context sensitive comparisons with -i.

The control can be specified in three ways:

On the command line, for example less -I bigfile.txt.

In the environment, for example export LESS=-i and later less bigfile.txt.

Within less itself, for example by starting less bigfile.txt and then typing -i.

edited Apr 11 at 16:21

answered Apr 10 at 18:53

roaima

46.2k758124

Hey, roaima. I think this is incorrect. ``` -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains uppercase letters, then that search does not ignore case. -I or --IGNORE-CASE Like -i, but searches ignore case even if the pattern contains uppercase letters. ``` From my experiments, it behaves as -I, not as -i.

– regex
Apr 10 at 23:14

1

You could also append |$A (which translates as or A after the end of the line) for your pattern to become case sensitive without having to the change the settings.

– Stéphane Chazelas
Apr 11 at 16:35

@StéphaneChazelas that's thrown me. I had thought $ was only special at the end of an RE (or RE clause), so $A would match a dollar and a capital letter, but A$ would match a capital at the end of a line. (Update: I can't even mimic this with perl, but definitely works with less.)

– roaima
Apr 11 at 16:50

@roaima, it's different between BRE and ERE, POSIX requires BRE $a to match on $a, and ERE $a to not match ($ to match the end of the subject wherever it's found). In Perl/PCRE, $ matches at the end of the subject or before a trailing line delimiter at the end of the subject, or if the m flag is enabled ((?m)) at the end of the subject or before any line delimiter in the subject.

– Stéphane Chazelas
Apr 11 at 17:26

add a comment |

It's explained in the man page for less.

The default action for REs is to ignore case if there are no uppercase characters present, but to act case-sensitively otherwise.

There are three modes available within less:

Case context dependent: a search or RE without uppercase characters is considered to be case-insensitive, but a search or RE containing at least one uppercase character is considered to be case-sensitive. Examples: abc will match abc and aBC, but aBc will only match aBc and not abc or ABC. This is the default setting.

Case sensitive: a search or RE pays full regard to the case of any letter. Example: abC will match only abC and not abc or ABC.

Case insensitive: a search or RE pays no regard to the case of any letter. Example: abC will match any of abc, abC, or ABC.

You can toggle case sensitive comparisons with -I, and case context sensitive comparisons with -i.

The control can be specified in three ways:

On the command line, for example less -I bigfile.txt.

In the environment, for example export LESS=-i and later less bigfile.txt.

Within less itself, for example by starting less bigfile.txt and then typing -i.

edited Apr 11 at 16:21

answered Apr 10 at 18:53

roaima

46.2k758124

Hey, roaima. I think this is incorrect. ``` -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains uppercase letters, then that search does not ignore case. -I or --IGNORE-CASE Like -i, but searches ignore case even if the pattern contains uppercase letters. ``` From my experiments, it behaves as -I, not as -i.

– regex
Apr 10 at 23:14

1

You could also append |$A (which translates as or A after the end of the line) for your pattern to become case sensitive without having to the change the settings.

– Stéphane Chazelas
Apr 11 at 16:35

@StéphaneChazelas that's thrown me. I had thought $ was only special at the end of an RE (or RE clause), so $A would match a dollar and a capital letter, but A$ would match a capital at the end of a line. (Update: I can't even mimic this with perl, but definitely works with less.)

– roaima
Apr 11 at 16:50

@roaima, it's different between BRE and ERE, POSIX requires BRE $a to match on $a, and ERE $a to not match ($ to match the end of the subject wherever it's found). In Perl/PCRE, $ matches at the end of the subject or before a trailing line delimiter at the end of the subject, or if the m flag is enabled ((?m)) at the end of the subject or before any line delimiter in the subject.

– Stéphane Chazelas
Apr 11 at 17:26

add a comment |

It's explained in the man page for less.

The default action for REs is to ignore case if there are no uppercase characters present, but to act case-sensitively otherwise.

There are three modes available within less:

Case context dependent: a search or RE without uppercase characters is considered to be case-insensitive, but a search or RE containing at least one uppercase character is considered to be case-sensitive. Examples: abc will match abc and aBC, but aBc will only match aBc and not abc or ABC. This is the default setting.

Case sensitive: a search or RE pays full regard to the case of any letter. Example: abC will match only abC and not abc or ABC.

Case insensitive: a search or RE pays no regard to the case of any letter. Example: abC will match any of abc, abC, or ABC.

You can toggle case sensitive comparisons with -I, and case context sensitive comparisons with -i.

The control can be specified in three ways:

On the command line, for example less -I bigfile.txt.

In the environment, for example export LESS=-i and later less bigfile.txt.

Within less itself, for example by starting less bigfile.txt and then typing -i.

edited Apr 11 at 16:21

answered Apr 10 at 18:53

roaima

46.2k758124

It's explained in the man page for less.

The default action for REs is to ignore case if there are no uppercase characters present, but to act case-sensitively otherwise.

There are three modes available within less:

Case context dependent: a search or RE without uppercase characters is considered to be case-insensitive, but a search or RE containing at least one uppercase character is considered to be case-sensitive. Examples: abc will match abc and aBC, but aBc will only match aBc and not abc or ABC. This is the default setting.

Case sensitive: a search or RE pays full regard to the case of any letter. Example: abC will match only abC and not abc or ABC.

Case insensitive: a search or RE pays no regard to the case of any letter. Example: abC will match any of abc, abC, or ABC.

You can toggle case sensitive comparisons with -I, and case context sensitive comparisons with -i.

The control can be specified in three ways:

On the command line, for example less -I bigfile.txt.

In the environment, for example export LESS=-i and later less bigfile.txt.

Within less itself, for example by starting less bigfile.txt and then typing -i.

edited Apr 11 at 16:21

answered Apr 10 at 18:53

roaima

46.2k758124

edited Apr 11 at 16:21

answered Apr 10 at 18:53

roaima

46.2k758124

answered Apr 10 at 18:53

roaima

46.2k758124

answered Apr 10 at 18:53

roaima

46.2k758124

Hey, roaima. I think this is incorrect. ``` -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains uppercase letters, then that search does not ignore case. -I or --IGNORE-CASE Like -i, but searches ignore case even if the pattern contains uppercase letters. ``` From my experiments, it behaves as -I, not as -i.

– regex
Apr 10 at 23:14

1

You could also append |$A (which translates as or A after the end of the line) for your pattern to become case sensitive without having to the change the settings.

– Stéphane Chazelas
Apr 11 at 16:35

@StéphaneChazelas that's thrown me. I had thought $ was only special at the end of an RE (or RE clause), so $A would match a dollar and a capital letter, but A$ would match a capital at the end of a line. (Update: I can't even mimic this with perl, but definitely works with less.)

– roaima
Apr 11 at 16:50

@roaima, it's different between BRE and ERE, POSIX requires BRE $a to match on $a, and ERE $a to not match ($ to match the end of the subject wherever it's found). In Perl/PCRE, $ matches at the end of the subject or before a trailing line delimiter at the end of the subject, or if the m flag is enabled ((?m)) at the end of the subject or before any line delimiter in the subject.

– Stéphane Chazelas
Apr 11 at 17:26

add a comment |

Hey, roaima. I think this is incorrect. ``` -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains uppercase letters, then that search does not ignore case. -I or --IGNORE-CASE Like -i, but searches ignore case even if the pattern contains uppercase letters. ``` From my experiments, it behaves as -I, not as -i.

– regex
Apr 10 at 23:14

1

You could also append |$A (which translates as or A after the end of the line) for your pattern to become case sensitive without having to the change the settings.

– Stéphane Chazelas
Apr 11 at 16:35

@StéphaneChazelas that's thrown me. I had thought $ was only special at the end of an RE (or RE clause), so $A would match a dollar and a capital letter, but A$ would match a capital at the end of a line. (Update: I can't even mimic this with perl, but definitely works with less.)

– roaima
Apr 11 at 16:50

@roaima, it's different between BRE and ERE, POSIX requires BRE $a to match on $a, and ERE $a to not match ($ to match the end of the subject wherever it's found). In Perl/PCRE, $ matches at the end of the subject or before a trailing line delimiter at the end of the subject, or if the m flag is enabled ((?m)) at the end of the subject or before any line delimiter in the subject.

– Stéphane Chazelas
Apr 11 at 17:26

Hey, roaima. I think this is incorrect. ``` -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains uppercase letters, then that search does not ignore case. -I or --IGNORE-CASE Like -i, but searches ignore case even if the pattern contains uppercase letters. ``` From my experiments, it behaves as -I, not as -i.

– regex
Apr 10 at 23:14

You could also append |$A (which translates as or A after the end of the line) for your pattern to become case sensitive without having to the change the settings.

– Stéphane Chazelas
Apr 11 at 16:35

@StéphaneChazelas that's thrown me. I had thought $ was only special at the end of an RE (or RE clause), so $A would match a dollar and a capital letter, but A$ would match a capital at the end of a line. (Update: I can't even mimic this with perl, but definitely works with less.)

– roaima
Apr 11 at 16:50

@roaima, it's different between BRE and ERE, POSIX requires BRE $a to match on $a, and ERE $a to not match ($ to match the end of the subject wherever it's found). In Perl/PCRE, $ matches at the end of the subject or before a trailing line delimiter at the end of the subject, or if the m flag is enabled ((?m)) at the end of the subject or before any line delimiter in the subject.

– Stéphane Chazelas
Apr 11 at 17:26

add a comment |

Pretty sure you can get around that by using -i or +i in order to set less to default.

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

answered Apr 10 at 18:49

6d6d

212

New contributor

Thank you, 6b6b.

– regex
Apr 10 at 18:59

add a comment |

Pretty sure you can get around that by using -i or +i in order to set less to default.

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

answered Apr 10 at 18:49

6d6d

212

New contributor

Thank you, 6b6b.

– regex
Apr 10 at 18:59

add a comment |

Pretty sure you can get around that by using -i or +i in order to set less to default.

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

answered Apr 10 at 18:49

6d6d

212

New contributor

Pretty sure you can get around that by using -i or +i in order to set less to default.

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

answered Apr 10 at 18:49

6d6d

212

New contributor

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

edited Apr 10 at 19:44

Jeff Schaller♦

45k1164147

answered Apr 10 at 18:49

6d6d

212

New contributor

answered Apr 10 at 18:49

6d6d

212

answered Apr 10 at 18:49

6d6d

212

New contributor

6d6d is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

Thank you, 6b6b.

– regex
Apr 10 at 18:59

add a comment |

Thank you, 6b6b.

– regex
Apr 10 at 18:59

Thank you, 6b6b.

– regex
Apr 10 at 18:59

add a comment |

regex is a new contributor. Be nice, and check out our Code of Conduct.

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