I have a skeleton text file with placeholder strings:
blah blah blah
blah $PLACEHOLDER_1$
blah
$PLACEHOLDER_2$
and so on. Specific \"form\" of
I just stumbled upon this question because I was just looking for the exact same, and I found envsubst(1)
.
You can use envsubst if you don't mind using environment variables:
PLACEHOLDER_1='string 1' PLACEHOLDER_2='multiline
string
2' envsubst < output.template
If you have a lot of variables you can store them in a file and just source
it (remember to use export
at the end of the sourced file!)
Building on the previous answer, perhaps use an array and compute the sed string?
#!/bin/sh
PLACEHOLDER[0]='string 1'
PLACEHOLDER[1]='multiline
string
2'
s="sed -i "
for(( i=0 ; i<${#PLACEHOLDER[*]} ; i++ )) ; do
echo ${PLACEHOLDER[$i]}
s=$s"s/PLACEHOLDER_$i/${PLACEHOLDER[$i]}/g;"
done
echo $s
Seems to fail on the multi-line strings, though.
I don't know how portable Bash arrays might be. Above snippet tested with "GNU bash, version 3.2.17(1)-release (i386-apple-darwin9.0)"
My bash only solution:
TEMPLATE='
foo
$var1
bar
$var2'
eval "echo \"$TEMPLATE\""
You can still use sed to do the replace in a single pass. You just need to specify all the replacements in one command.
eg.
sed -i 's/PLACEHOLDER_1/string 1/g;s/PLACEHOLDER_2/string 2/g' <file>
Here's a way to do it without sed:
First, a slightly modified template file in which the placeholders are bash variables:
blah blah blah
blah $PLACEHOLDER_1
blah
$PLACEHOLDER_2
And the script:
#! /bin/sh
templatefile=output.template
outputfile=output.txt
PLACEHOLDER_1='string 1'
PLACEHOLDER_2='multiline
string
2'
# DONE: Generate file output.txt from file output.template
# using placeholders above.
echo "$(eval "echo \"$(cat $templatefile)\"")" > $outputfile
Here's a version that demonstrates a template contained within the script, but with a twist. It also demonstrates default values, which can also be used in the template file version, plus you can do math in the template:
#! /bin/sh
template='blah blah blah
blah $PLACEHOLDER_1
blah
${PLACEHOLDER_2:-"some text"} blah ${PLACEHOLDER_3:-"some
lines
of
text"} and the total is: $((${VAL_1:-0} + ${VAL_2:-0}))'
# default operands to zero (or 1) to prevent errors due to unset variables
outputfile=output.txt
# gears spin, bells ding, values for placeholders are computed
PLACEHOLDER_1='string 1'
PLACEHOLDER_2='multiline
string
2'
VAL_1=2
VAL_2=4
unset PLACEHOLDER_3 # so we can trigger one of the defaults
# Generate file output.txt from variable $template
# using placeholders above.
echo "$(eval "echo \"$template\"")" > $outputfile
No sed, no loops, just hairy nesting and quotes. I'm pretty sure all the quoting will protect you from malicious stuff in a template file, but I'm not going to guarantee it.