Can't escape a dot using backslash, Why?

Som Shekhar Mukherjee

10/27/22, 8:48 AM

So, following are the commands are I ran:

$ ~/Documents: touch ball.txt bool-txt bowl.txt bull.txt
$ ~/Documents: ls . | grep b..l\.txt
ball.txt
bool-txt
bowl.txt
bull.txt

I wasn't expecting bool-txt to be present in the output, because I have escaped the dot but its still not considering it a literal dot. Where am I going wrong?

1 + 3

grep

pipe

qwr

10/27/22, 8:50 AM

that might be shell escaping, try putting it in a string

qwr

10/27/22, 8:51 AM

also in general parsing ls is error prone, but probably not relevant to this question

Som Shekhar Mukherjee

10/27/22, 8:53 AM

Yeah this `ls . | grep b..l\\.txt` works and also this `ls . | b..l"\.".txt`. Is this what you meant? Could you explain mean what is happening here or point me to relevant resources. @qwr

Score:5

Ubuntu

qwr

10/27/22, 8:59 AM

I'm sure this is a duplicate of some question but I can't find it. On Unix SE https://unix.stackexchange.com/questions/583428/why-do-i-have-to-quote-an-escaped-character-in-a-regular-expression-for-grep-bu

When you use grep b..l\.txt, the shell converts \. into . so grep receives b..l.txt, then it interprets . as any character.

To prevent this, the easiest method is giving grep a string like grep 'b..l\.txt', then the shell won't escape the dot. Note that single quotes and double quotes do different things in bash but that doesn't matter in this case. Alternatively, use double backslash so the shell escapes the backslash as a literal character and grep correctly receives \..

0 + 2

Som Shekhar Mukherjee

10/27/22, 9:01 AM

Also could explain this "also in general parsing ls is error prone"? It would be really helpful.

qwr

10/27/22, 9:04 AM

long story https://unix.stackexchange.com/q/128985/171025

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Can't escape a dot using backslash, Why?

TH: ไม่สามารถหลีกเลี่ยงจุดโดยใช้แบ็กสแลช เพราะเหตุใด

RO: Nu se poate scăpa de un punct folosind bara oblică inversă, de ce?

RU: Не удается избежать точки с помощью обратной косой черты. Почему?

VI: Không thể thoát dấu chấm bằng dấu gạch chéo ngược, Tại sao?

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