Bash script to replace multiple predefined variables in a template file to create a new file. Test files included.

ReplaceVars.sh

#!/bin/bash 
echo "Replacing variables in file."

InFile="${1:-Test.txt}"
InFileName="${InFile%.*}"
InFileExt=${InFile#"$InFileName"}
OutFile=${2:-"${InFileName}_out${InFileExt}"}
InVar=${3:-VarValues.txt}

if [ ! -f $InFile ] || [ ! -f $InVar ] ; then 
	[ ! -f $InFile ] && echo "Error: InFile '$InFile' not found!"
	[ ! -f $InVar ] && echo "Error: VarFile '$InVar' not found!"
	echo ""
	echo "  Usage: ${0} InFile [ OutFile [VarFile] ]"
	echo "    InFile defaults to 'Test.txt'"
	echo "    OutFile defaults to appends '_out' to Infile, like this 'Test_old.txt'"
	echo "    VarFile defaults to 'VarValues.txt'"
	echo "    VarFile must contain set of 'CurrentVar=NewValue', #comments are allowed"
	echo "    InFile must contain '$CurrentVar$' strings, which will be substituted with 'NewValue' strings"
	echo "    Suggested usage:"
	echo "                     ${0} version.tbl version.h version.vars"
	exit 1
fi


# Cleanup
rm -f ${OutFile}

# Import known variables
VarCounter=0
while IFS= read -r line  || [ -n "$line" ]; do
	var=${line%%=*}
	val=${line#*=}
	if [[ ${var} == \#* ]]; then
		# Skip comments.
		continue
	fi
	if [[ -n $val ]]; then	# Variable Value must be non-empty.
		#Split line up into two variable arrays.
		eval ReplaceVar[VarCounter]="${var}"
		eval ReplaceVal[VarCounter]="${val}"
	fi
	VarCounter=$((VarCounter+1))
done < ${InVar}
echo "Read $((VarCounter)) variables"

# Copy source to destination if no variables were found to replace.
if [[ ${VarCounter} == 0 ]]; then
	# No variables to replace.
	cp ${InFile} ${OutFile}
	echo "Copied ${InFile} to ${OutFile}"
	echo "Done"
	exit 0
fi

# Read input, replacing the known variables, and output to OutFile
LineCounter=0
while IFS= read -r line  || [ -n "$line" ]; do
	for i in "${!ReplaceVar[@]}"; do
		line=${line//\$${ReplaceVar[i]}\$/${ReplaceVal[i]}}
	done
	echo "${line}" >> ${OutFile}
#	echo "${LineCounter}:${line}"
	LineCounter=$((LineCounter+1))
done < ${InFile}
echo "Processed ${LineCounter} lines in ${InFile}, and created ${OutFile}."
echo "Done."
exit 0

Test.txt

dsxzczxc $test1$ lasdfhlashdklas <aLÆSKJLÆSAHJ
$test2$ lasdfhlashdklas >aLÆSKJLÆSAHJ
lasdfhlashdklas >aLÆSKJLÆSAHJ$test3$$lasdfhlashdklas >aLÆSKJLÆSAHJ
lasdfhlashdklas >aLÆSKJLÆSAHJ$test4$

Test_out.txt

dsxzczxc _____test1_string___ lasdfhlashdklas <aLÆSKJLÆSAHJ
_____test2_string___ lasdfhlashdklas >aLÆSKJLÆSAHJ
lasdfhlashdklas >aLÆSKJLÆSAHJ_____test3_string___$lasdfhlashdklas >aLÆSKJLÆSAHJ
lasdfhlashdklas >aLÆSKJLÆSAHJ_____test4_string___

VarValues.txt

#List of variables to replace.
test1=_____test_one_string___
test2=_____test_two_string___
test3=_____test_three_string___
test4=_____test_four_string___