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Kane Billiot avatar Ubuntu

How to save specific lines of command line outputs

cn flag
Kane Billiot

I have an executable that produces the following to the terminal:

---Start---
Some text
More text
-1.
1.
0.39
10
-199
some more text
   Complete
---End---

I want to write only the numerical values in the terminal to a file. Right now, I am using

./executable 2>&1 | grep -vE 'S|M|s|^[--]|^[ ]' | tee log.txt

This seems to do what I want. Specifically, by using -v, I am explicitly stating what to exclude. However, this seems rather inefficient since I would have to add in the whole alphabet (both upper and lower case) to make sure that only numerical values get added to the log.txt file.

Is there a better write all of the numerical values (positive and negative) to a file?

73
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in flag
pbhj
Are you looking for a new regex? '^[0-9-].*$' will capture whole lines starting with a digit or minus-sign. Or use \d for digits, see eg [regular-expressions.info](https://www.regular-expressions.info/quickstart.html).
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hr flag
steeldriver
See for example [grep - Only allow floating points regex](https://unix.stackexchange.com/questions/397784/only-allow-floating-points-regex) and [Matching Floating Point Numbers with a Regular Expression](https://www.regular-expressions.info/floatingpoint.html)
2
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bac0n avatar
cn flag
bac0n
@pbhj the dot should be moved into the character class `'^[0-9.-]*$'` but as @steeldrive pointed out may not be enough.
0
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waltinator avatar
it flag
waltinator
Unless it's at the beginning of the expression, "`-`" is confused with the "range" ("`[0-9]`") operator. Use "`^[-.0-9]+`". You could also make use of `grep`'s "`-o`" option to output only the matched string.
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bac0n avatar
cn flag
bac0n
@waltinator that will match Start and End too...
1
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in flag
pbhj
@bac0n, none of the numbers start with a decimal point, my regex was to find lines starting with a digit or "-", the rest of the line can be any character. If you put the dot inside the range selector then you'll need to escape it because "." means "any character once", also it might be needed to escape the "-" (ie "\-") but if it's not between two other characters I've found the regex engine to always recognise it as a separate character. Depends on the version of grep (or other program); mine works for the given input in GNU Grep 3.6; tested on Kali.
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bac0n avatar
cn flag
bac0n
@pbhj first, the pattern will match the start and end tags too. Next, a dot inside `[.]` brackets are interpreted literally (no need to escape). If a hyphen is placed first or last in the range class it will also be interpreted literally.
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in flag
pbhj
You might be correct on the literal dot, not something I have experience with, but the hyphen not needing escaping certainly works, like I said, tested on GNU Grep. It matches the start because he's looking for lines with a digit at the start, it matches the end because the sample shows he wants the whole of the lines that have a digit (or minus) on. Try it.
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bac0n avatar
cn flag
bac0n
`echo '---End---' | grep '^[0-9-].*$'`
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Score:1
elmclose avatar Ubuntu
cn flag
elmclose

You simply need to exclude lines that have text in them. Use this grep in your command:

grep -v '[A-Za-z]'
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