My bash script needs to read the variables from a text file that contains hundreds of variables, most of which conform to standard bash variable syntax (e.g., VAR1=VALUE1). However, a few lines in this file can be problematic, and I hope to find a simple solution to reading them into bash.

Here's what the file looks like:

VAR6=VALUE 6 #a comment
VAR9=a name with spaces

The rules about the file structure include:

  • one variable (with value) per line
  • the assignment (=) has no spaces around it
  • the variable name is in the first column (unless it is a comment line)
  • comments can follow the value (after #)
  • the values can include spaces, parens, slashes, commas, and other chars
  • the values can be floating point numbers (2.1), integers, true/false, or strings.
  • string values are not quoted, and they can be a thousand chars long or longer
  • the variable name contains only letters and underscores UPDATE: and numbers.

Most of the variables are of a type that would just allow me to source the file into my bash script. But those few problematic ones dictate a different solution. I'm not sure how to read them.

  • Can you just put the RHS into single quotes?
    – Ketan
    Commented Feb 22, 2014 at 2:05
  • @Ketan - how do you mean? I can't change the text file with the variables.
    – MountainX
    Commented Feb 22, 2014 at 2:15
  • You don't have to change the original text file, run it through sed and put the output in a new file and source it.
    – Ketan
    Commented Feb 22, 2014 at 2:17
  • @Ketan - that sounds like it should work... can you provide an answer with example code? The devil is often in the details, especially with bash. Thank you.
    – MountainX
    Commented Feb 22, 2014 at 2:20

2 Answers 2


While you can transform this file to be a shell snippet, it's tricky. You need to make sure that all shell special characters are properly quoted.

The easiest way to do that is to put single quotes around the value and replace single quotes inside the value by '\''. You can then put the result into a temporary file and source that file.

sed <"config-file" >"$script" \
  -e '/^[A-Z_a-z][A-Z_a-z]*=/ !d' \
  -e s/\'/\'\\\\\'\'/g \
  -e s/=/=\'/ -e s/\$/\'/

I recommend doing the parsing directly in the shell instead. The complexity of the code is about the same, but there are two major benefits: you avoid the need for a temporary file, and the risk that you accidentally got the quoting wrong and end up executing a part of a line as a shell snippet (something like dangerous='$(run me)'). You also get a better chance at validating potential errors.

while IFS= read -r line; do
  line=${line%%#*}  # strip comment (if any)
  case $line in
      case $var in
          echo "Warning: invalid variable name $var ignored" >&2
      if eval '[ -n "${'$var'+1}" ]'; then
        echo "Warning: variable $var already set, redefinition ignored" >&2
      eval $var='"$line"'
done <"config-file"
  • I'm using your recommended (2nd) method. Works great. Is there an easy way to check for a variable naming collision during this while-loop? With this approach it seems like that check might be appropriately incorporated.
    – MountainX
    Commented Feb 23, 2014 at 0:43
  • Regarding name collisions, I guess I could use eval IMPORTED_$var='"$line"' but I would rather first check for collisions and not change/prefix the variable names.
    – MountainX
    Commented Feb 23, 2014 at 0:53
  • @MountainX See my edit. Commented Feb 23, 2014 at 0:55
  • BTW, I made a mistake regarding the variable name convention. The standard letters, numbers and underscores are allowed. So the char class expression should be [!A-Z_a-z0-9].
    – MountainX
    Commented Feb 23, 2014 at 0:57
  • @Gilles-re: name collisions. I guess the principle of your solution is that null +1 is still null. So if the result of that expression is not null, the variable name exists. Correct?
    – MountainX
    Commented Feb 23, 2014 at 1:03

Assuming your contents are in a file x.txt, you can use a sed expression:

sed -e 's/#.*//' -e 's/=.*$/="&"/g' -e 's/=//2' x.txt

First expression puts everything after the = sign in quotes. Second expression removes extra = sign and the third expression removes everything between # and " as they are comments.

Following will quote RHS into single quotes:

sed -e "s/#.*//" -e "s/=.*$/='&'/g" -e "s/=//2" x.txt
  • The result is VAR1"=value1"
    – MountainX
    Commented Feb 22, 2014 at 2:33
  • Yep, realized that and made an update. See if it works now.
    – Ketan
    Commented Feb 22, 2014 at 2:34
  • This doesn't handle values containing " or '. Commented Feb 22, 2014 at 23:13
  • It also handles comments incorrectly (the leading quote is kept, the trailing quote is deleted together with the #). BTW, it's probably useful to delete the comment together with any preceding whitespace.
    – Uwe
    Commented Feb 22, 2014 at 23:27
  • @Gilles It does retain single and double quotes in the RHS. @Uwe I made changes to treat comments correctly. Everything after # is now removed first.
    – Ketan
    Commented Feb 22, 2014 at 23:39

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