Re: Escaping grep

On 17/04/2021 08.36, bodiccea wrote:
> On Sun, 21 Feb 2021 15:35:55 -0600, "Michael F. Stemper"
> <[email protected]> wrote:
> 
>> I wanted to see which LaTeX packages I was using for a particular
>> project, so I did:
>>
>> user@host$ grep -h "\\usep" *tex | sort | uniq
>> % \usepackage{array} % for math mode columns in tabular
>> % \usepackage{graphicx}
>> % \usepackage{longtable}
>> % \usepackage{mathrsfs} % for mathscr
>> % \usepackage{tikz-cd} % for commutative diagrams
>> \usepackage{amsmath} % for implication and align*
>> \usepackage{amssymb} % for black-board set names
>> \usepackage{fancyhdr}
>> \usepackage{geometry}
>> \usepackage{parskip}
>> user@host$
>>
>> However, that showed unused packages as well. So I tried
>> anchoring my grep to the beginning of the line, and got:
>>
>> user@host$ grep -h "^\\usep" *tex | sort | uniq
>> user@host$
>>
>> Why isn't this working? What am I overlooking? How
>> should I have said it?
> 
> There is no issue with the grep expression itself. The problem is
> with bash handling of strings: You use " (double quotes) around
> your expression, asking bash to interpret the contents.
> 
> bash will replace "^\\usep" with "^\usep" *before passing it to grep*.
> grep then will remove special meaning for following char (u) - no
> special meaning in this case.
> The result is that grep will just look for lines starting with "u".

Thank you. I've been using various *IX variants for three decades now
and I still can't get the single-quote v double-quote distinction
through my head.

> You have 2 solutions:
> 1) use quotes instead of double quotes: '^\\usep', so that bash does
> not change anything.

Works fine, lasts a long time!

> Sorry for late answer, I just joined this group.
> 
> And yes, it is a pure 'bash' question, not a 'grep' question as I saw in
> another answer :)

Thought so!

-- 
Michael F. Stemper
Outside of a dog, a book is man's best friend.
Inside of a dog, it's too dark to read.