On Sun, Oct 22, 2023 at 04:33:12PM +0000, Albretch Mueller wrote:
> I am trying to use a one liner like:
> cat "${IFL}" | grep "${DESC_DIR}" | tail -c+$_DESC_DIR
> but this one liner repeats the output and the tail
Brevity is not the measure of goodness. When you write a shell script,
it's *OK* to use more than one line.
Also, please stop using ALL_CAPS variable names for internal script
variables. ALL_CAPS names are by convention reserved for the environment.
Names with a leading underscore are allowed, but should be used only
when you need something special. There's nothing special in the code
above to merit a variable name like _DESC_DIR.
Also also, useless use of cat <https://mywiki.wooledge.org/BashFAQ/119>.
Finally, mixing up _DESC_DIR and DESC_DIR is probably not helping you.
> Say the lines of text in IFL are:
> [info] 123XYZ:
> /media/user/1234qwer/Algebraic_Geometry04/20231022040239/Uppsala_Algebra/45_16.3_45MEB5h5H9Y.description
> [info] 123XYZ:
> /media/user/1234qwer/Algebraic_Geometry04/20231022040239/Uppsala_Algebra/46_17.1_LE_gl5RcDnY.description
> [info] 123XYZ:
> /media/user/1234qwer/Algebraic_Geometry04/20231022040239/Göttsche/17_9jKzwoBGFs8.description
> [info] 123XYZ:
> /media/user/1234qwer/Algebraic_Geometry04/20231022040239/Göttsche/18_plOUIOo91lI.description
> [info] 123XYZ:
> /media/user/1234qwer/Algebraic_Geometry04/20231022040239/Göttsche/19_TJ7yAiq8gEw.description
> [info] 123XYZ:
> /media/user/1234qwer/Algebraic_Geometry04/20231022040239/Göttsche/20_UMBEgb14uqw.description
>
> I know the prefix:
> [info] 123XYZ: /media/user/1234qwer/Algebraic_Geometry04/20231022040239/
>
> I need as output:
>
> Uppsala_Algebra/45_16.3_45MEB5h5H9Y
> Uppsala_Algebra/46_17.1_LE_gl5RcDnY
> Göttsche/17_9jKzwoBGFs8
> Göttsche/18_plOUIOo91lI
> Göttsche/19_TJ7yAiq8gEw
> Göttsche/20_UMBEgb14uqw
Yay! Sample input! That makes it nice and easy.
#!/bin/bash
inputfile=${1-/whatever}
prefix='[info] 123XYZ:
/media/user/1234qwer/Algebraic_Geometry04/20231022040239/'
while IFS= read -r line; do
printf '%s\n' "${line#"$prefix"}"
done < <(grep -F -- "$prefix" "$inputfile")
Yes, I could make it shorter. I could even use that functional approach
where you pipe grep and sed together, which some people think is the only
way to write shell code. It could actually be done in a single sed
command (but you'd have to convert the prefix string to a regular
expression first).
I chose not to do any of those, for two reasons:
1) To make it easier to read and understand.
2) To make it possible to do more than simply *printing* the suffixes.
If your script wants to do something with those suffixes, more than
simply printing them on the screen, then the script I wrote is a much
better starting point. You can stick additional commands inside the
loop body to do whatever you need.
On Sun, Oct 22, 2023 at 11:07:46AM -0600, Charles Curley wrote:
> Bash has built in operators to extract this sort of thing. Greg
> Wooledge will know what they are called. Something like:
>
> fspec="/exp/home1/abc.txt"
> filename="${fspec##*/}" # get filename
> dirname="${fspec%/*}" # get directory/path name
>
> That doesn't do exactly what you want, but comes close.
Those are called Parameter Expansions. For a beginner-friendly intro,
please see <https://mywiki.wooledge.org/BashFAQ/100>.
