Bash + read variables & values from file by bash script

bashevallinuxshell-scriptvariable

I have the following file variable and values

# more file.txt
export worker01="sdg sdh sdi sdj sdk"
export worker02="sdg sdh sdi sdj sdm"
export worker03="sdg sdh sdi sdj sdf"

I perform source in order to read the variable

# source file.txt

example:

echo $worker01
sdg sdh sdi sdj sdk

until now every thing is perfect

but now I want to read the variables from the file and print the values
by simple bash loop I will read the second field and try to print value of the variable

#  for i in ` sed s'/=/ /g'  /tmp/file.txt | awk '{print $2}' `
   do  
   echo $i
   declare var="$i"
   echo $var
   done

but its print only the variable and not the values

worker01
worker01
worker02
worker02
worker03
worker03

expected output:

worker01
sdg sdh sdi sdj sdk
worker02
sdg sdh sdi sdj sdm
worker03
sdg sdh sdi sdj sdf

Best Answer

You have export worker01="sdg sdh sdi sdj sdk", then you replace = with a space to get export worker01 "sdg sdh sdi sdj sdk". The space separated fields in that are export, worker01, "sdg, sdh, etc.

It's probably better to split on =, and remove the quotes, so with just the shell:

$ while IFS== read -r key val ; do
    val=${val%\"}; val=${val#\"}; key=${key#export };
    echo "$key = $val";
  done < vars
worker01 = sdg sdh sdi sdj sdk
worker02 = sdg sdh sdi sdj sdm
worker03 = sdg sdh sdi sdj sdf

key contains the variable name, val the value. Of course this doesn't actually parse the input, it just removes the double quotes if they happen to be there.

Related Solutions

Bash – Why Isn’t ‘set’ Behaving as Expected

set MONGODB="/usr/local/mongodb/bin"

This is not a variable assignment. (It is one in C shell (csh, tcsh), but not in Bourne-style shells (sh, ash, bash, ksh, zsh, …).) This is a call to the set built-in, which sets the positional parameters, i.e. $1, $2, etc. Try running this command in a terminal, then echo $1.

To assign a value to a shell variable, just write

MONGODB="/usr/local/mongodb/bin"

This creates a shell variable (also called a (named) parameter), which you can access with $MONGODB. The variable remains internal to the shell unless you've exported it with export MONGODB. If exported, the variable is also visible to all processes started by that shell, through the environment. You can condense the assignment and the export into a single line:

export MONGODB="/usr/local/mongodb/bin"

For what you're doing, there doesn't seem to be a need for MONGODB outside the script, and PATH is already exported (once a variable is exported, if you assign a new value, it is reflected in the environment). So you can write:

MONGODB="/usr/local/mongodb/bin"    
PATH=${PATH}:${MONGODB}

Bash – Read non-bash variables from a file into bash script

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.

script=$(mktemp)
sed <"config-file" >"$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 $line in
    *=*)
      var=${line%%=*}
      case $var in
        *[!A-Z_a-z]*)
          echo "Warning: invalid variable name $var ignored" >&2
          continue;;
      esac
      if eval '[ -n "${'$var'+1}" ]'; then
        echo "Warning: variable $var already set, redefinition ignored" >&2
        continue
      fi
      line=${line#*=}
      eval $var='"$line"'
  esac
done <"config-file"

Best Answer

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Bash – Why Isn’t ‘set’ Behaving as Expected

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