I'm trying to compare the contents of two files in a bash script.
local_file=$(cat my_local_file.txt)
remote_file=$(curl -s "http://example.com/remote-file.txt")
if [ local_file == remote_file ]; then
echo "Files are the same"
else
echo "Files are different. Here is the diff:"
diff <(echo "$local_file") <(echo "$remote_file")
fi
When I run the script, I see that I have a syntax error:
./bin/check_files.sh: line 8: syntax error near unexpected token `('
./bin/check_files.sh: line 8: ` diff <(echo "$local_file") <(echo "$remote_file")'
What am I doing wrong? How can I display a diff of these two strings from a bash script?
Process substitution is a bash feature, which is usually not available in /bin/sh which is meant to be POSIX compatible.
Make sure to use the following shebang line if you want to run the script as an executable:
#!/bin/bash
instead of
#!/bin/sh
or use
bash script.sh
instead of
sh script.sh
if you run it like that
To make the script work with POSIX conform shells I would just download the file and compare it against the local file. Remove the downloaded file after the diff.
In addition to the <(command) (process substitution) syntax issue, your code if [ local_file == remote_file ] compares the literal strings local_file and remote_file, rather than the content of the variables. You need $local_file and $remote_file to compare the contents. Need to enclose them in double quotes to prevent word splitting issues.
You could do this:
#!/bin/bash
local_file=$(< my_local_file.txt) # this is more efficient than $(cat file)
remote_file=$(curl -s "http://example.com/remote-file.txt")
if [ "$local_file" = "$remote_file" ]; then
echo "Files are the same"
else
echo "Files are different. Here is the diff:"
diff <(printf '%s' "$local_file") <(printf '%s' "$remote_file")
fi
As stated by #dimo414, the limitation here is that the command substitution $(...) removes trailing newlines and that would cause a problem. So, it is better to download the remote file and compare it with the local file:
local_file=my_local_file.txt
curl -s "http://example.com/remote-file.txt" -o remote_file
if diff=$(diff -- "$local_file" remote_file); then
echo "Files are the same"
else
echo "Files are different. Here is the diff:"
printf '%s' "$diff"
fi
You can also use the following command:
cmp -b "File_1.txt" "File_2.txt"
To get started, here's the script I'm running to get the offending string:
# sed finds all sourced file paths from inputted file.
#
# while reads each match output from sed to $SOURCEFILE variable.
# Each should be a file path, or a variable that represents a file path.
# Any variables found should be expanded to the full path.
#
# echo and calls are used for demonstractive purposes only
# I intend to do something else with the path once it's expanded.
PATH_SOME_SCRIPT="/path/to/bash/script"
while read -r SOURCEFILE; do
echo "$SOURCEFILE"
"$SOURCEFILE"
$SOURCEFILE
done < <(cat $PATH_SOME_SCRIPT | sed -n -e "s/^\(source\|\.\|\$include\) //p")
You may also wish to use the following to test this out as mock data:
[ /path/to/bash/script ]
#!/bin/bash
source "$HOME/bash_file"
source "$GLOBAL_VAR_SCRIPT_PATH"
echo "No cow powers here"
For the tl;dr crew, basically the while loop spits out the following on the mock data:
"$HOME/bash_file"
bash: "$HOME/bash_file": no such file or directory
bash: "$HOME/bash_file": no such file or directory
"$GLOBAL_VAR_SCRIPT_PATH"
"$GLOBAL_VAR_SCRIPT_PATH": command not found
"$GLOBAL_VAR_SCRIPT_PATH": command not found
My question is, can you get the variable to expand correctly, e.g., print "/home//bash_file" and "/expanded/variable/path"? I should also state that although eval works I do not intend to use it because of its potential insecurities.
Protip that any variable value used in cat | sed would be available globally, including to the calling script, so it's not because the script cannot call the variable value.
FIRST SOLUTION ATTEMPT
Using anubhava's envsubst solution:
SOMEVARIABLE="/home/nick/.some_path"
while read -r SOURCEFILE; do
echo "$SOURCEFILE"
envsubst <<< "$SOURCEFILE";
done < <(echo -e "\"\$SOMEVARIABLE\"\n\"$HOME/.another_file\"")
This outputs the following:
"$SOMEVARIABLE"
""
"/home/nick/.another_file"
"/home/nick/.another_file"
Unfortunately, it does not expand the variable! Oh dear :(
SECOND SOLUTION ATTEMPT
Based upon the first attempt:
export SOMEVARIABLE="/home/nick/.some_path"
while read -r SOURCEFILE; do
echo "$SOURCEFILE"
envsubst <<< "$SOURCEFILE";
done < <(echo -e "\"\$SOMEVARIABLE\"\n\"$HOME/.another_file\"")
unset SOMEVARIABLE
which produces the results we wanted without eval and without messing with global variables (for too long anyway), hoorah!
Good runner-ups were further suggested using eval (although potentially unsafe) which can be found in this answer and here (link courtesy of anubhava's extended comments).
My question is, can you get the variable to expand correctly, e.g., print "/home//bash_file" and "/expanded/variable/path"?
Yes you can use envsubst program, that substitutes the values of environment variables:
while read -r sourceFile; do
envsubst <<< "$sourceFile"
done < <(sed -n "s/^\(source\|\.\|\$include\) //p" "$PATH_SOME_SCRIPT")
I think you are asking how to recursively expand variables in bash. Try
expanded=$(eval echo $SOURCEFILE)
inside your loop. eval runs the expanded command you give it. Since $SOURCEFILE isn't in quotes, it will be expanded to, e.g., $HOME/whatever. Then the eval will expand the $HOME before passing it to echo. echo will print the result, and expanded=$(...) will put the printed result in $expanded.
I'm trying to write a "phone home" script, which will log the exact command line (including any single or double quotes used) into a MySQL database. As a backend, I have a cgi script which wraps the database. The scripts themselves call curl on the cgi script and include as parameters various arguments, including the verbatim command line.
Obviously I have quite a variety of quote escaping to do here and I'm already stuck at the bash stage. At the moment, I can't even get bash to print verbatim the arguments provided:
Desired output:
$ ./caller.sh -f -hello -q "blah"
-f hello -q "blah"
Using echo:
caller.sh:
echo "$#"
gives:
$ ./caller.sh -f -hello -q "blah"
-f hello -q blah
(I also tried echo $# and echo $*)
Using printf %q:
caller.sh:
printf %q $#
printf "\n"
gives:
$ ./caller.sh -f hello -q "blah"
-fhello-qblah
(I also tried print %q "$#")
I would welcome not only help to fix my bash problem, but any more general advice on implementing this "phone home" in a tidier way!
There is no possible way you can write caller.sh to distinguish between these two commands invoked on the shell:
./caller.sh -f -hello -q "blah"
./caller.sh -f -hello -q blah
There are exactly equivalent.
If you want to make sure the command receives special characters, surround the argument with single quotes:
./caller.sh -f -hello -q '"blah"'
Or if you want to pass just one argument to caller.sh:
./caller.sh '-f -hello -q "blah"'
You can get this info from the shell history:
function myhack {
line=$(history 1)
line=${line#* }
echo "You wrote: $line"
}
alias myhack='myhack #'
Which works as you describe:
$ myhack --args="stuff" * {1..10} $PATH
You wrote: myhack --args="stuff" * {1..10} $PATH
However, quoting is just the user's way of telling the shell how to construct the program's argument array. Asking to log how the user quotes their arguments is like asking to log how hard the user punched the keys and what they were wearing at the time.
To log a shell command line which unambiguously captures all of the arguments provided, you don't need any interactive shell hacks:
#!/bin/bash
line=$(printf "%q " "$#")
echo "What you wrote would have been indistinguishable from: $line"
I understand you want to capture the arguments given by the caller.
Firstly, quotes used by the caller are used to protect during the interpretation of the call. But they do not exist as argument.
An example: If someone call your script with one argument "Hello World!" with two spaces between Hello and World. Then you have to protect ALWAYS $1 in your script to not loose this information.
If you want to log all arguments correctly escaped (in the case where they contains, for example, consecutive spaces...) you HAVE to use "$#" with double quotes. "$#" is equivalent to "$1" "$2" "$3" "$4" etc.
So, to log arguments, I suggest the following at the start of the caller:
i=0
for arg in "$#"; do
echo "arg$i=$arg"
let ++i
done
## Example of calls to the previous script
#caller.sh '1' "2" 3 "4 4" "5 5"
#arg1=1
#arg2=2
#arg3=3
#arg4=4 4
#arg5=5 5
#Flimm is correct, there is no way to distinguish between arguments "foo" and foo, simply because the quotes are removed by the shell before the program receives them. What you need is "$#" (with the quotes).
I'm writing a script to automate creating configuration files for Apache and PHP for my own webserver. I don't want to use any GUIs like CPanel or ISPConfig.
I have some templates of Apache and PHP configuration files. Bash script needs to read templates, make variable substitution and output parsed templates into some folder. What is the best way to do that? I can think of several ways. Which one is the best or may be there are some better ways to do that? I want to do that in pure Bash (it's easy in PHP for example)
How to replace ${} placeholders in a text file?
template.txt:
The number is ${i}
The word is ${word}
script.sh:
#!/bin/sh
#set variables
i=1
word="dog"
#read in template one line at the time, and replace variables
#(more natural (and efficient) way, thanks to Jonathan Leffler)
while read line
do
eval echo "$line"
done < "./template.txt"
BTW, how do I redirect output to external file here? Do I need to escape something if variables contain, say, quotes?
Using cat & sed for replacing each variable with its value:
Given template.txt (see above)
Command:
cat template.txt | sed -e "s/\${i}/1/" | sed -e "s/\${word}/dog/"
Seems bad to me because of the need to escape many different symbols and with many variables the line will be tooooo long.
Can you think of some other elegant and safe solution?
Try envsubst
$ cat envsubst-template.txt
Variable FOO is (${FOO}).
Variable BAR is (${BAR}).
$ FOO=myfoo
$ BAR=mybar
$ export FOO BAR
$ cat envsubst-template.txt | envsubst
Variable FOO is (myfoo).
Variable BAR is (mybar).
A heredoc is a builtin way to template a conf file.
STATUS_URI="/hows-it-goin"; MONITOR_IP="10.10.2.15";
cat >/etc/apache2/conf.d/mod_status.conf <<EOF
<Location ${STATUS_URI}>
SetHandler server-status
Order deny,allow
Deny from all
Allow from ${MONITOR_IP}
</Location>
EOF
Regarding yottsa's answer: envsubst was new to me. Fantastic.
You can use this:
perl -p -i -e 's/\$\{([^}]+)\}/defined $ENV{$1} ? $ENV{$1} : $&/eg' < template.txt
to replace all ${...} strings with corresponding enviroment variables (do not forget to export them before running this script).
For pure bash this should work (assuming that variables do not contain ${...} strings):
#!/bin/bash
while read -r line ; do
while [[ "$line" =~ (\$\{[a-zA-Z_][a-zA-Z_0-9]*\}) ]] ; do
LHS=${BASH_REMATCH[1]}
RHS="$(eval echo "\"$LHS\"")"
line=${line//$LHS/$RHS}
done
echo "$line"
done
. Solution that does not hang if RHS references some variable that references itself:
#!/bin/bash
line="$(cat; echo -n a)"
end_offset=${#line}
while [[ "${line:0:$end_offset}" =~ (.*)(\$\{([a-zA-Z_][a-zA-Z_0-9]*)\})(.*) ]] ; do
PRE="${BASH_REMATCH[1]}"
POST="${BASH_REMATCH[4]}${line:$end_offset:${#line}}"
VARNAME="${BASH_REMATCH[3]}"
eval 'VARVAL="$'$VARNAME'"'
line="$PRE$VARVAL$POST"
end_offset=${#PRE}
done
echo -n "${line:0:-1}"
WARNING: I do not know a way to correctly handle input with NULs in bash or preserve the amount of trailing newlines. Last variant is presented as it is because shells “love” binary input:
read will interpret backslashes.
read -r will not interpret backslashes, but still will drop the last line if it does not end with a newline.
"$(…)" will strip as many trailing newlines as there are present, so I end … with ; echo -n a and use echo -n "${line:0:-1}": this drops the last character (which is a) and preserves as many trailing newlines as there was in the input (including no).
I agree with using sed: it is the best tool for search/replace. Here is my approach:
$ cat template.txt
the number is ${i}
the dog's name is ${name}
$ cat replace.sed
s/${i}/5/
s/${name}/Fido/
$ sed -f replace.sed template.txt > out.txt
$ cat out.txt
the number is 5
the dog's name is Fido
I have a bash solution like mogsie but with heredoc instead of herestring to allow you to avoid escaping double quotes
eval "cat <<EOF
$(<template.txt)
EOF
" 2> /dev/null
Try eval
I think eval works really well. It handles templates with linebreaks, whitespace, and all sorts of bash stuff. If you have full control over the templates themselves of course:
$ cat template.txt
variable1 = ${variable1}
variable2 = $variable2
my-ip = \"$(curl -s ifconfig.me)\"
$ echo $variable1
AAA
$ echo $variable2
BBB
$ eval "echo \"$(<template.txt)\"" 2> /dev/null
variable1 = AAA
variable2 = BBB
my-ip = "11.22.33.44"
This method should be used with care, of course, since eval can execute arbitrary code. Running this as root is pretty much out of the question. Quotes in the template need to be escaped, otherwise they will be eaten by eval.
You can also use here documents if you prefer cat to echo
$ eval "cat <<< \"$(<template.txt)\"" 2> /dev/null
#plockc provoded a solution that avoids the bash quote escaping issue:
$ eval "cat <<EOF
$(<template.txt)
EOF
" 2> /dev/null
Edit: Removed part about running this as root using sudo...
Edit: Added comment about how quotes need to be escaped, added plockc's solution to the mix!
Edit Jan 6, 2017
I needed to keep double quotes in my configuration file so double escaping double quotes with sed helps:
render_template() {
eval "echo \"$(sed 's/\"/\\\\"/g' $1)\""
}
I can't think of keeping trailing new lines, but empty lines in between are kept.
Although it is an old topic, IMO I found out more elegant solution here: http://pempek.net/articles/2013/07/08/bash-sh-as-template-engine/
#!/bin/sh
# render a template configuration file
# expand variables + preserve formatting
render_template() {
eval "echo \"$(cat $1)\""
}
user="Gregory"
render_template /path/to/template.txt > path/to/configuration_file
All credits to Grégory Pakosz.
Instead of reinventing the wheel go with envsubst
Can be used in almost any scenario, for instance building configuration files from environment variables in docker containers.
If on mac make sure you have homebrew then link it from gettext:
brew install gettext
brew link --force gettext
./template.cfg
# We put env variables into placeholders here
this_variable_1 = ${SOME_VARIABLE_1}
this_variable_2 = ${SOME_VARIABLE_2}
./.env:
SOME_VARIABLE_1=value_1
SOME_VARIABLE_2=value_2
./configure.sh
#!/bin/bash
cat template.cfg | envsubst > whatever.cfg
Now just use it:
# make script executable
chmod +x ./configure.sh
# source your variables
. .env
# export your variables
# In practice you may not have to manually export variables
# if your solution depends on tools that utilise .env file
# automatically like pipenv etc.
export SOME_VARIABLE_1 SOME_VARIABLE_2
# Create your config file
./configure.sh
I'd have done it this way, probably less efficient, but easier to read/maintain.
TEMPLATE='/path/to/template.file'
OUTPUT='/path/to/output.file'
while read LINE; do
echo $LINE |
sed 's/VARONE/NEWVALA/g' |
sed 's/VARTWO/NEWVALB/g' |
sed 's/VARTHR/NEWVALC/g' >> $OUTPUT
done < $TEMPLATE
If you want to use Jinja2 templates, see this project: j2cli.
It supports:
Templates from JSON, INI, YAML files and input streams
Templating from environment variables
A longer but more robust version of the accepted answer:
perl -pe 's;(\\*)(\$([a-zA-Z_][a-zA-Z_0-9]*)|\$\{([a-zA-Z_][a-zA-Z_0-9]*)\})?;substr($1,0,int(length($1)/2)).($2&&length($1)%2?$2:$ENV{$3||$4});eg' template.txt
This expands all instances of $VAR or ${VAR} to their environment values (or, if they're undefined, the empty string).
It properly escapes backslashes, and accepts a backslash-escaped $ to inhibit substitution (unlike envsubst, which, it turns out, doesn't do this).
So, if your environment is:
FOO=bar
BAZ=kenny
TARGET=backslashes
NOPE=engi
and your template is:
Two ${TARGET} walk into a \\$FOO. \\\\
\\\$FOO says, "Delete C:\\Windows\\System32, it's a virus."
$BAZ replies, "\${NOPE}s."
the result would be:
Two backslashes walk into a \bar. \\
\$FOO says, "Delete C:\Windows\System32, it's a virus."
kenny replies, "${NOPE}s."
If you only want to escape backslashes before $ (you could write "C:\Windows\System32" in a template unchanged), use this slightly-modified version:
perl -pe 's;(\\*)(\$([a-zA-Z_][a-zA-Z_0-9]*)|\$\{([a-zA-Z_][a-zA-Z_0-9]*)\});substr($1,0,int(length($1)/2)).(length($1)%2?$2:$ENV{$3||$4});eg' template.txt
Here's another pure bash solution:
it's using heredoc, so:
complexity doesn't increase because of additionaly required syntax
template can include bash code
that also allows you to indent stuff properly. See below.
it doesn't use eval, so:
no problems with the rendering of trailing empty lines
no problems with quotes in the template
$ cat code
#!/bin/bash
LISTING=$( ls )
cat_template() {
echo "cat << EOT"
cat "$1"
echo EOT
}
cat_template template | LISTING="$LISTING" bash
Input:
$ cat template (with trailing newlines and double quotes)
<html>
<head>
</head>
<body>
<p>"directory listing"
<pre>
$( echo "$LISTING" | sed 's/^/ /' )
<pre>
</p>
</body>
</html>
Output:
<html>
<head>
</head>
<body>
<p>"directory listing"
<pre>
code
template
<pre>
</p>
</body>
</html>
Here is another solution: generate a bash script with all the variables and the contents of the template file, that script would look like this:
word=dog
i=1
cat << EOF
the number is ${i}
the word is ${word}
EOF
If we feed this script into bash it would produce the desired output:
the number is 1
the word is dog
Here is how to generate that script and feed that script into bash:
(
# Variables
echo word=dog
echo i=1
# add the template
echo "cat << EOF"
cat template.txt
echo EOF
) | bash
Discussion
The parentheses opens a sub shell, its purpose is to group together all the output generated
Within the sub shell, we generate all the variable declarations
Also in the sub shell, we generate the cat command with HEREDOC
Finally, we feed the sub shell output to bash and produce the desired output
If you want to redirect this output into a file, replace the last line with:
) | bash > output.txt
Taking the answer from ZyX using pure bash but with new style regex matching and indirect parameter substitution it becomes:
#!/bin/bash
regex='\$\{([a-zA-Z_][a-zA-Z_0-9]*)\}'
while read line; do
while [[ "$line" =~ $regex ]]; do
param="${BASH_REMATCH[1]}"
line=${line//${BASH_REMATCH[0]}/${!param}}
done
echo $line
done
If using Perl is an option and you're content with basing expansions on environment variables only (as opposed to all shell variables), consider Stuart P. Bentley's robust answer.
This answer aims to provide a bash-only solution that - despite use of eval - should be safe to use.
The goals are:
Support expansion of both ${name} and $name variable references.
Prevent all other expansions:
command substitutions ($(...) and legacy syntax `...`)
arithmetic substitutions ($((...)) and legacy syntax $[...]).
Allow selective suppression of variable expansion by prefixing with \ (\${name}).
Preserve special chars. in the input, notably " and \ instances.
Allow input either via arguments or via stdin.
Function expandVars():
expandVars() {
local txtToEval=$* txtToEvalEscaped
# If no arguments were passed, process stdin input.
(( $# == 0 )) && IFS= read -r -d '' txtToEval
# Disable command substitutions and arithmetic expansions to prevent execution
# of arbitrary commands.
# Note that selectively allowing $((...)) or $[...] to enable arithmetic
# expressions is NOT safe, because command substitutions could be embedded in them.
# If you fully trust or control the input, you can remove the `tr` calls below
IFS= read -r -d '' txtToEvalEscaped < <(printf %s "$txtToEval" | tr '`([' '\1\2\3')
# Pass the string to `eval`, escaping embedded double quotes first.
# `printf %s` ensures that the string is printed without interpretation
# (after processing by by bash).
# The `tr` command reconverts the previously escaped chars. back to their
# literal original.
eval printf %s "\"${txtToEvalEscaped//\"/\\\"}\"" | tr '\1\2\3' '`(['
}
Examples:
$ expandVars '\$HOME="$HOME"; `date` and $(ls)'
$HOME="/home/jdoe"; `date` and $(ls) # only $HOME was expanded
$ printf '\$SHELL=${SHELL}, but "$(( 1 \ 2 ))" will not expand' | expandVars
$SHELL=/bin/bash, but "$(( 1 \ 2 ))" will not expand # only ${SHELL} was expanded
For performance reasons, the function reads stdin input all at once into memory, but it's easy to adapt the function to a line-by-line approach.
Also supports non-basic variable expansions such as ${HOME:0:10}, as long as they contain no embedded command or arithmetic substitutions, such as ${HOME:0:$(echo 10)}
Such embedded substitutions actually BREAK the function (because all $( and ` instances are blindly escaped).
Similarly, malformed variable references such as ${HOME (missing closing }) BREAK the function.
Due to bash's handling of double-quoted strings, backslashes are handled as follows:
\$name prevents expansion.
A single \ not followed by $ is preserved as is.
If you want to represent multiple adjacent \ instances, you must double them; e.g.:
\\ -> \ - the same as just \
\\\\ -> \\
The input mustn't contain the following (rarely used) characters, which are used for internal purposes: 0x1, 0x2, 0x3.
There's a largely hypothetical concern that if bash should introduce new expansion syntax, this function might not prevent such expansions - see below for a solution that doesn't use eval.
If you're looking for a more restrictive solution that only supports ${name} expansions - i.e., with mandatory curly braces, ignoring $name references - see this answer of mine.
Here is an improved version of the bash-only, eval-free solution from the accepted answer:
The improvements are:
Support for expansion of both ${name} and $name variable references.
Support for \-escaping variable references that shouldn't be expanded.
Unlike the eval-based solution above,
non-basic expansions are ignored
malformed variable references are ignored (they don't break the script)
IFS= read -d '' -r lines # read all input from stdin at once
end_offset=${#lines}
while [[ "${lines:0:end_offset}" =~ (.*)\$(\{([a-zA-Z_][a-zA-Z_0-9]*)\}|([a-zA-Z_][a-zA-Z_0-9]*))(.*) ]] ; do
pre=${BASH_REMATCH[1]} # everything before the var. reference
post=${BASH_REMATCH[5]}${lines:end_offset} # everything after
# extract the var. name; it's in the 3rd capture group, if the name is enclosed in {...}, and the 4th otherwise
[[ -n ${BASH_REMATCH[3]} ]] && varName=${BASH_REMATCH[3]} || varName=${BASH_REMATCH[4]}
# Is the var ref. escaped, i.e., prefixed with an odd number of backslashes?
if [[ $pre =~ \\+$ ]] && (( ${#BASH_REMATCH} % 2 )); then
: # no change to $lines, leave escaped var. ref. untouched
else # replace the variable reference with the variable's value using indirect expansion
lines=${pre}${!varName}${post}
fi
end_offset=${#pre}
done
printf %s "$lines"
To follow up on plockc's answer on this page, here is a dash-suitable version, for those of you looking to avoid bashisms.
eval "cat <<EOF >outputfile
$( cat template.in )
EOF
" 2> /dev/null
Try shtpl
Perfect case for shtpl. (project of mine, so it is not widely in use and lacks in documentation. But here is the solution it offers anyhow. May you want to test it.)
Just execute:
$ i=1 word=dog sh -c "$( shtpl template.txt )"
Result is:
the number is 1
the word is dog
Have fun.
This page describes an answer with awk
awk '{while(match($0,"[$]{[^}]*}")) {var=substr($0,RSTART+2,RLENGTH -3);gsub("[$]{"var"}",ENVIRON[var])}}1' < input.txt > output.txt
# Usage: template your_file.conf.template > your_file.conf
template() {
local IFS line
while IFS=$'\n\r' read -r line ; do
line=${line//\\/\\\\} # escape backslashes
line=${line//\"/\\\"} # escape "
line=${line//\`/\\\`} # escape `
line=${line//\$/\\\$} # escape $
line=${line//\\\${/\${} # de-escape ${ - allows variable substitution: ${var} ${var:-default_value} etc
# to allow arithmetic expansion or command substitution uncomment one of following lines:
# line=${line//\\\$\(/\$\(} # de-escape $( and $(( - allows $(( 1 + 2 )) or $( command ) - UNSECURE
# line=${line//\\\$\(\(/\$\(\(} # de-escape $(( - allows $(( 1 + 2 ))
eval "echo \"${line}\"";
done < "$1"
}
This is the pure bash function adjustable to your liking, used in production and should not break on any input.
If it breaks - let me know.
You can also use bashible (which internally uses the evaluating approach described above/below).
There is an example, how to generate a HTML from multiple parts:
https://github.com/mig1984/bashible/tree/master/examples/templates
Look at simple variables substitution python script here: https://github.com/jeckep/vsubst
It is very simple to use:
python subst.py --props secure.properties --src_path ./templates --dst_path ./dist
Here's a bash function that preserves whitespace:
# Render a file in bash, i.e. expand environment variables. Preserves whitespace.
function render_file () {
while IFS='' read line; do
eval echo \""${line}"\"
done < "${1}"
}
Here's a modified perl script based on a few of the other answers:
perl -pe 's/([^\\]|^)\$\{([a-zA-Z_][a-zA-Z_0-9]*)\}/$1.$ENV{$2}/eg' -i template
Features (based on my needs, but should be easy to modify):
Skips escaped parameter expansions (e.g. \${VAR}).
Supports parameter expansions of the form ${VAR}, but not $VAR.
Replaces ${VAR} with a blank string if there is no VAR envar.
Only supports a-z, A-Z, 0-9 and underscore characters in the name (excluding digits in the first position).
You can also use printf to fill a template.
#!/bin/bash
IFS='' read -rd '' TEMPL <<-'EOB'
The number is %d
The word is "%s"
Birds of Massachusetts:
%s
EOB
N=12
WORD="Bird"
MULTILINE="Eastern Bluebirds
Common Grackles"
echo "START"
printf "${TEMPL}" ${N} ${WORD} "${MULTILINE}"
echo "END"
Here's the output, with quotes and whitespace intact:
START
The number is 12
The word is "Bird"
Birds of Massachusetts:
Eastern Bluebirds
Common Grackles
END