A Journal Through My Activities, Thoughts, and Notes
#grep #tips
## Basic Regular Expressions (BRE)
Basic Regular Expressions are the default regular expression syntax used by
Some key points about BRE:
- Metacharacters like
- The
- Alternation is done using
- Repetition operators like
For example, to match lines containing either "cat" or "dog" using BRE:
And to match lines with 3 to 6 digits:
The backslashes are necessary to use the grouping and repetition metacharacters in BRE syntax.
So in summary, BRE provides a more limited set of regex features compared to ERE, but is still very powerful for common text matching tasks. The main difference is the need to escape certain metacharacters in BRE.
One thing I would to mention here is that most metacharacters in Basic Regular Expressions (BRE) need to be escaped, but the
### Historical Context
In the early days of Unix, the
### Why Not Escape
Escaping every special character would make BRE more verbose and less readable, especially for simple patterns. By treating
### Example
For instance, to match any number of characters before or after a specific string, you can use:
This will match any line containing "pattern" followed by zero or more characters.
### Summary
While most metacharacters in BRE require escaping, the
## Basic Regular Expressions (BRE)
Basic Regular Expressions are the default regular expression syntax used by
grep when no special options are provided. BRE uses a more limited set of metacharacters compared to Extended Regular Expressions (ERE).Some key points about BRE:
- Metacharacters like
+, ?, |, (, ) are treated as literal characters and need to be escaped with a backslash (\) to use their special meaning.- The
$$ and $$ constructs are used for grouping in BRE, instead of just ( and ) as in ERE.- Alternation is done using
\| instead of just |.- Repetition operators like
* and \{n,m\} are used to match zero or more and ranges of repetitions respectively.For example, to match lines containing either "cat" or "dog" using BRE:
grep 'cat\|dog' filename
And to match lines with 3 to 6 digits:
grep '\([0-9]\{3,6\}\)' filename
The backslashes are necessary to use the grouping and repetition metacharacters in BRE syntax.
So in summary, BRE provides a more limited set of regex features compared to ERE, but is still very powerful for common text matching tasks. The main difference is the need to escape certain metacharacters in BRE.
One thing I would to mention here is that most metacharacters in Basic Regular Expressions (BRE) need to be escaped, but the
* character does not. This might seem inconsistent, but it's due to historical reasons and the way BRE was designed.### Historical Context
In the early days of Unix, the
grep command was developed, and it used BRE as its default syntax. At that time, the * character was already a special character in many programming languages and shell scripts, often used for wildcard matching. To avoid conflicts and make BRE more intuitive for users familiar with shell globbing, the designers of grep decided to treat the * character as a special character without needing an escape.### Why Not Escape
*?Escaping every special character would make BRE more verbose and less readable, especially for simple patterns. By treating
* as a special character without an escape, it simplifies common tasks like matching any number of characters (including zero) before or after another character.### Example
For instance, to match any number of characters before or after a specific string, you can use:
grep 'pattern*' filename
This will match any line containing "pattern" followed by zero or more characters.
### Summary
While most metacharacters in BRE require escaping, the
* character is an exception due to its historical significance and the desire to keep BRE syntax simple and intuitive. This makes it easier for users to learn and use basic regular expressions without needing to worry about escaping every special character.#网友语录
说起来我在澳洲的第一个困惑经历就来自这方面。
那天老师问：在中国，你生病了是去医院还是去看医生。
我心里想：这不是一回事吗？
老师心里想：看起来她没有听懂我的问题，我换个说法试试。
😂
解释：在澳洲和新西兰，看医生是指看社区诊所的全科医生，要先预约，要付诊费，但等待时间短。去医院一般是去急诊。比如全科医生已经下班了，这时候就要去医院。医院分公立和私立。公立不要钱，但通常要排队排很久，非紧急病情排几个小时很正常。还有一种是24hours诊所，非工签，非PR，非公民有紧急情况，一般只能去24Hours诊所，收费相对贵（以基督城为例，普通诊所$54一次，但24Hours要$170一次）。
说起来我在澳洲的第一个困惑经历就来自这方面。
那天老师问：在中国，你生病了是去医院还是去看医生。
我心里想：这不是一回事吗？
老师心里想：看起来她没有听懂我的问题，我换个说法试试。
😂
解释：在澳洲和新西兰，看医生是指看社区诊所的全科医生，要先预约，要付诊费，但等待时间短。去医院一般是去急诊。比如全科医生已经下班了，这时候就要去医院。医院分公立和私立。公立不要钱，但通常要排队排很久，非紧急病情排几个小时很正常。还有一种是24hours诊所，非工签，非PR，非公民有紧急情况，一般只能去24Hours诊所，收费相对贵（以基督城为例，普通诊所$54一次，但24Hours要$170一次）。
前几天婉拒了一个机会，因为问过了自己的内心，并不想更换赛道，虽然那个赛道我很喜欢玩。我更满足现在的生活，担心以那个方向为业会挤掉我的业余项目，也担心会毁掉我对它本来的兴趣。
年岁渐长就会变得保守？并不。我问过自己的内心了，就是不想要。
年岁渐长就会变得保守？并不。我问过自己的内心了，就是不想要。
#网友语录 #非洲
1880 年代后，欧洲列强加速了对非洲大陆的瓜分，几乎将整个非洲划分完毕。只有埃塞俄比亚 Ethiopia 和利比里亚 Liberia 成功保持了独立。埃塞俄比亚以其强大的军事实力和坚强的民族意识抵抗了意大利的侵略，地形险峻和复杂的气候也阻碍了外军的入侵。埃塞俄比亚的地图离远了乍一看像是临海，但其实一点都没有，它是全球人口最多的内陆国家，有一亿人口。早期基督教从公元 1 世纪开始就已经在埃塞俄比亚传播了，现在国民大多数信仰基督教。埃塞俄比亚还是咖啡的原产地。利比里亚创立的初衷是为被解放的黑人提供一个新的定居地，受到了美国的庇护，得以避免被欧洲列强吞并，但其独立地位仍依赖于美国的保护，因为其国力相对较弱。Liberia 得名于自由 liberty 和解放 liberation，国旗和宪法仿效美国，首都蒙罗维亚 Monrovia 纪念的是美国总统 James Monroe。利比里亚的官方语言是英语，我好几次在博洛尼亚搭讪到说英语的非洲人都是利比里亚来的。
1880 年代后，欧洲列强加速了对非洲大陆的瓜分，几乎将整个非洲划分完毕。只有埃塞俄比亚 Ethiopia 和利比里亚 Liberia 成功保持了独立。埃塞俄比亚以其强大的军事实力和坚强的民族意识抵抗了意大利的侵略，地形险峻和复杂的气候也阻碍了外军的入侵。埃塞俄比亚的地图离远了乍一看像是临海，但其实一点都没有，它是全球人口最多的内陆国家，有一亿人口。早期基督教从公元 1 世纪开始就已经在埃塞俄比亚传播了，现在国民大多数信仰基督教。埃塞俄比亚还是咖啡的原产地。利比里亚创立的初衷是为被解放的黑人提供一个新的定居地，受到了美国的庇护，得以避免被欧洲列强吞并，但其独立地位仍依赖于美国的保护，因为其国力相对较弱。Liberia 得名于自由 liberty 和解放 liberation，国旗和宪法仿效美国，首都蒙罗维亚 Monrovia 纪念的是美国总统 James Monroe。利比里亚的官方语言是英语，我好几次在博洛尼亚搭讪到说英语的非洲人都是利比里亚来的。
#grep #tips
The -o option in grep stands for "only matching." When this option is used, grep will print only the parts of the lines that match the specified pattern, rather than the entire line. This is particularly useful when you want to extract specific substrings from lines of text.
The
### Key Differences with Extended Regular Expressions
When using
1. Metacharacters: In ERE, the following metacharacters are treated as special without needing to be escaped:
-
-
-
-
2. Example Usage:
- To match either "cat" or "dog", you can use:
- To match one or more digits, you can use:
3. Combining with Other Options: You can combine
The -o option in grep stands for "only matching." When this option is used, grep will print only the parts of the lines that match the specified pattern, rather than the entire line. This is particularly useful when you want to extract specific substrings from lines of text.
The
-E option in grep enables the use of Extended Regular Expressions (ERE) in the pattern. This allows for more powerful and flexible pattern matching compared to basic regular expressions (BRE), which is the default behavior of grep.### Key Differences with Extended Regular Expressions
When using
-E, you can utilize additional metacharacters and constructs that are not available in basic regular expressions. Here are some of the key features of ERE:1. Metacharacters: In ERE, the following metacharacters are treated as special without needing to be escaped:
-
+ : Matches one or more occurrences of the preceding element.-
? : Matches zero or one occurrence of the preceding element.-
| : Acts as a logical OR between expressions.-
() : Groups patterns for applying quantifiers or for alternation.2. Example Usage:
- To match either "cat" or "dog", you can use:
grep -E "cat|dog" filename
- To match one or more digits, you can use:
grep -E "[0-9]+"
3. Combining with Other Options: You can combine
-E with other options like -i for case insensitivity or -o to print only the matching parts: grep -Eio "cat|dog" filename#swift #教程
https://m.youtube.com/playlist?list=PLXM8k1EWy5kiAD0o69R00b7I62ZVUyfJJ
我只看完第一个视频就决定推荐它了。如果你零基础并对编程感兴趣，这是一个不可多得的资源。
https://m.youtube.com/playlist?list=PLXM8k1EWy5kiAD0o69R00b7I62ZVUyfJJ
我只看完第一个视频就决定推荐它了。如果你零基础并对编程感兴趣，这是一个不可多得的资源。
#网友语录 #recipe
发明用电饭锅煮意面的这位网友，我崇拜你。真的，凭什么意面就非得用水煮开了才能调味啊，它凭什么就不能像做焖饭一样直接和蔬菜、芝士、熟肉、意面酱和一点儿水自己组成意面？就这种圆筒的螺旋的意面，它多么适合做成焖面啊，我甚至想搞点扁豆和肉丝来焖它。亲测可行，方便省事儿。
Reference: https://mastodon.social/@inklingsdaily/113069324432944325
发明用电饭锅煮意面的这位网友，我崇拜你。真的，凭什么意面就非得用水煮开了才能调味啊，它凭什么就不能像做焖饭一样直接和蔬菜、芝士、熟肉、意面酱和一点儿水自己组成意面？就这种圆筒的螺旋的意面，它多么适合做成焖面啊，我甚至想搞点扁豆和肉丝来焖它。亲测可行，方便省事儿。
Reference: https://mastodon.social/@inklingsdaily/113069324432944325
#网友语录
加拿大小孩闹，群众烦不烦？烦得要命。别管孩子多大，群众不吭声，没人人觉得父母不管，该死。因为 you don't know what's going on with the kid.并不是每一个有问题的孩子都是可以看出来的。一般设定是父母有尽力，但是，就是有无能为力的时候。走开，戴上耳机，特别热心的过去问问能不能帮忙，或者安慰一下父母。贵国跟加拿大，有个最最基础的区别。加拿大从人好的方面看待一件事，贵国从人的恶劣方面看待一件事，他也没办法，和他就是故意的。不同的是，在加拿大“他就是故意的”到一定程度，会有警察来收拾他。所以，你且认为他也是没办法好了。
加拿大小孩闹，群众烦不烦？烦得要命。别管孩子多大，群众不吭声，没人人觉得父母不管，该死。因为 you don't know what's going on with the kid.并不是每一个有问题的孩子都是可以看出来的。一般设定是父母有尽力，但是，就是有无能为力的时候。走开，戴上耳机，特别热心的过去问问能不能帮忙，或者安慰一下父母。贵国跟加拿大，有个最最基础的区别。加拿大从人好的方面看待一件事，贵国从人的恶劣方面看待一件事，他也没办法，和他就是故意的。不同的是，在加拿大“他就是故意的”到一定程度，会有警察来收拾他。所以，你且认为他也是没办法好了。
