Using cat to write a file containing bash commands-CodePudding

Consider the following bash scripts:

#!/bin/bash
cat << EOF > file
$@
VAR=`cat somefile`
EOF

I want to write a file called file such that $@ is evaluated but cat something is not. In other words I want the output to look like this:

Arg1 Arg2 Arg3 Arg4 
VAR=`cat something`

If I use 'EOF' instead of EOF, then nothing gets evaluated, but I want $@ to be evaluated.

CodePudding user response：

Have you tried escaping the characters? Using "\`":

cat <<EOF > file
$@
VAR=\`cat testfile\`
echo \$VAR
> EOF

Here is the file content:

cat file

VAR=`cat testfile`
echo $VAR

Then execute it:

./file
Hi!

CodePudding user response：

If the variable to be expanded is at the beginning or at the end of the heredoc then you could use a quoted heredoc grouped with other printing instructions. also, expanding variables in foreign code is dangerous if you don't implement the proper escaping.

#!/bin/bash
{
# here I suppose that "$@" contains a command and it's arguments
printf '%q ' "$@"
echo

cat <<'EOF'
VAR=$( < testfile )
echo "$VAR"
EOF
} > file.sh