Bash: Find and replace using Parameter Expansion

Question

I want to replace the input,

find_string: @include circle-progress(38px, 30px, #4eb630)

and output,

Output_string: @include circle-progress(38px, 30px)

using ${find_string//pattern/replacement_string} where pattern is , , #[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]?([A-Fa-f0-9]?([A-Fa-f0-9]?([A-Fa-f0-9])))' that I supply.

In the code below, simply the line matching pattern is printed i.e find_string, when I read lines of code from a file, whereas I want the output_string to be printed.

pattern="@include circle-progress\(([0-9]{1,3}px, ){2}#[A-Fa-f0-9]
{3,6}\)" /*regex the matches find_string*/

replace_glob=', #[A-Fa-f0-9][A-Fa-f0-9][A-Fa-f0-9]?([A-Fa-f0-9]?([A-
Fa-f0-9]?([A-Fa-f0-9])))' /*glob pattern in the string to be replaced*/

while IFS='' read -r line || [[ -n "$line" ]]; do
   if [[ $line =~ $pattern ]] 
   then
      echo "${line//$replace_glob/}" 
   fi
done < "$1"

So basically your requirement is remove the part #4eb630 from the input string right? — Inian
– Inian, Commented Dec 22, 2017 at 10:04
@Inian Yes, That is what I want, using Parameter Expansion only — HarshvardhanSharma
– HarshvardhanSharma, Commented Dec 22, 2017 at 10:13
You can't use parameter expansion of type ${source/orig/repl/}, the variables orig and repl cannot be vaiables, they can just be strings. You need to use sed for replacement — Inian
– Inian, Commented Dec 22, 2017 at 10:34
@Inian The same concept works if I execute commands echo "${source//$replace_glob/}" with just a single source in interactive mode. It replaces @include circle-progress(38px, 30px, #4eb630) with @include circle-progress(38px, 30px). — HarshvardhanSharma
– HarshvardhanSharma, Commented Dec 22, 2017 at 10:40
Use awk or sed; this is the type of task they were created to handle. — chepner
– chepner, Commented Dec 22, 2017 at 15:03

Nahuel Fouilleul · Accepted Answer · 2017-12-22 13:16:55Z

3

The pattern in parameter expansion is not a regular expression but follows the same rules as glob pattern matching:

* : matches any character sequence
? : matches any character
[..] : any character in set
[^..] or [!..] : any character not in set

with shell option : shopt -s extglob, some more features but less than regular expressions

@(..|..) : match any once
?(..|..) : match any 0 or 1 times
*(..|..) : match any 0 or more times
!(..) : matches all except

However bash supports some basic regex, following should work:

string='@include circle-progress(38px, 30px, #4eb630)'
pattern='@include circle-progress\([ ]*[0-9]{1,3}px,[ ]*[0-9]{1,3}px(,[ ]*#[A-Fa-f0-9]{3,6}[ ]*)\)'
[[ $string =~ $pattern ]] && echo "${string//"${BASH_REMATCH[1]}"}"

edited Dec 22, 2017 at 13:16

answered Dec 22, 2017 at 13:07

Nahuel Fouilleul

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Ben · Accepted Answer · 2017-12-22 10:37:58Z

0

You can simply use sed

echo $line | sed 's/\(@include circle-progress([0-9]\{1,3\}px, [0-9]\{1,3\}px\), #[a-fA-F0-9]\{3,6\})/\1)/'

answered Dec 22, 2017 at 10:37

Ben

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