bash extended regex if statement

Question

Trying to match any string that looks like {% extends "file.txt" %}, using the following code:

local FILE_REG="(\.{0,2}\/)*([a-zA-Z0-9_]*|\/[a-zA-Z0-9_]*)*[a-zA-Z0-9_]*\.[a-zA-Z0-9_]*"
local EXTENDS_REG='{%\s*extends\s*".*"\s*%}'

local extends=0
local filename="$1"

echo $EXTENDS_REG;
while read -r line ; do
  if [[ "$line" =~ "{%\s*extends\s*\".*\"\s*%}" ]] ; then
    echo "true: $line";
  else
    echo "false: $line";
  fi;
done < $filename

The if statement fails to return true on the first line of the following:

{% extends "base.tsh" %}
{% block my_block %}
  echo "Hello World from inherit.tsh!"
{% endblock %}

I have verified my regex on regex101.com and the pattern on line 2 matches the string perfectly, while replacing the ".*" by $FILE_REG matches the previous string with "file.txt" being replaced by any valid /path/to/file_with_extension.txt.

I have tried numerous variations of the EXTENDS_REG in the if statement, including:

if [[ "$line" =~ "$EXTENDS_REG" ]] (variable)
if [[ "$line" =~ $EXTENDS_REG ]] (variable, no quotes)
if [[ "$line" =~ '{%\s*extends\s*".*"\s*%}' ]] (single quotes around regex)
if [[ "$line" =~ '{%\s*extends\s*"'$FILE_REG'"\s*%}' ]] (composite + single quotes)
if [[ "$line" =~ {%\s*extends\s*\".*\"\s*%} ]] (no quotes)

but none have worked. I suspect the if regex match to be too limited to read the regex properly within bash.

Anyone has any solution? Optimally I am looking for something efficient, and that does not rely on external binaries except grep, awk, sed and al. No python, ruby, perl, etc. please ;)

Thanks for your help!

Martin Konecny · Accepted Answer · 2015-08-15 03:06:58Z

4

line='{% extends "file.txt" %}'
if [[ $line =~ \{%[[:space:]]*extends[[:space:]]*\".*\"[[:space:]]*%\} ]]

In bash replace character classes such as \s with those of the form [[:class:]].

Here's a definitive list.

answered Aug 15, 2015 at 3:06

Martin Konecny

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3 Comments

Philippe Hebert Over a year ago

Thanks, would never have found that out myself. +1 for the source too. Would you know why using your version of the regex in a variable doesn't work? Aka EXTEND_REG=\{%[[:space:]]*extends[[:space:]]*\".*\"[[:space:]]*%\} and [[ $line =~ "$EXTEND_REG" ]] or [[ $line =~ $EXTEND_REG ]]? Is it because the $ conflicts with the regex eval?

Martin Konecny Over a year ago

Try EXTEND_REG='\{%[[:space:]]*extends[[:space:]]*\".*\"[[:space:]]*%\}' and then [[ $line =~ $EXTEND_REG ]]

Philippe Hebert Over a year ago

It works indeed! Thanks that will allow me to make my code cleaner.

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