মডিউল পাঠ (3/4)
`m` পতাকা: বহুরেখা
With the m (multiline) flag the anchors ^ and $ change meaning:
they are no longer start/end of the entire string, but start/end of
each line. A line is delimited by \n (or by the start/end of the
string).
Pattern: ^Errore
Flag: gm
Sample: Errore: A\nInfo: B\nErrore: C
^^^^^^ ^^^^^^Without m it would match only Errore at the absolute start of the
sample (1 match). With m, it matches the start of every line (2
matches).
m does NOT change the dot
A common confusion: the m flag does NOT change the meaning of the dot
.. The dot still does NOT match \n even with m. To make the dot
match everything you need the s flag (covered in module 1).
m and s are orthogonal: you can use them together (ms), separately,
or neither.
Multiline flag and line-by-line processing
The m flag modifies the behavior of ^ and $ by making them match the start and end of each line (delimited by \\n) within a multiline text block, instead of looking only at the absolute start and end of the entire string.
Try it
Find every line that starts with `ERROR`. Each line is separated by \\n; use flags `g` and `m`.
ইঙ্গিত দেখান
The m flag makes ^ match the start of inner lines too, not only the absolute first character.
সমাধান 3 প্রচেষ্টার পরে উপলব্ধ
Review exercise
Find every line that ENDS with a period. Use the `$` anchor with flags `m` and `g`.
ইঙ্গিত দেখান
\\.$ with gm flags matches the period at the end of every line, not only at the end of the sample.
সমাধান 3 প্রচেষ্টার পরে উপলব্ধ
Additional challenge
Find all lines in a multiline log that start exactly with the string `ID:` followed by a digit.
ইঙ্গিত দেখান
Use ^ before ID: and make sure the m flag is active.
সমাধান 3 প্রচেষ্টার পরে উপলব্ধ