Ok, here is one I am struggling with as we speak. Echoing a echo command with a variable.
echo "creating new script file." echo "#!/bin/bash" > $servsfile echo "read -p "Please enter a service: " ser " >> $servfile echo "servicetest=`getsebool -a | grep ${ser}` " >> $servfile echo "if [ $servicetest > /dev/null ];then " >> $servfile echo "echo "we are now going to work with ${ser}" " >> $servfile echo "else" >> $servfile echo "exit 1" >> $servfile echo "fi" >> $servfile
My goal is create a script using echo commands then run it later. I just need to figure out how to echo echo/read commands while maintaining my variables.
edit: the variables need to transfer what's inside of them into the new file.
Use the -v flag with printf to assign a shell variable to store the data instead of printing it in standard output. The output prints the stored variable contents.
The immediate problem is you have is with quoting: by using double quotes ("..."
), your variable references are instantly expanded, which is probably not what you want.
Use single quotes instead - strings inside single quotes are not expanded or interpreted in any way by the shell.
(If you want selective expansion inside a string - i.e., expand some variable references, but not others - do use double quotes, but prefix the $
of references you do not want expanded with \
; e.g., \$var
).
However, you're better off using a single here-doc[ument], which allows you to create multi-line stdin
input on the spot, bracketed by two instances of a self-chosen delimiter, the opening one prefixed by <<
, and the closing one on a line by itself - starting at the very first column; search for Here Documents
in man bash
or at http://www.gnu.org/software/bash/manual/html_node/Redirections.html.
If you quote the here-doc delimiter (EOF
in the code below), variable references are also not expanded. As @chepner points out, you're free to choose the method of quoting in this case: enclose the delimiter in single quotes or double quotes, or even simply arbitrarily escape one character in the delimiter with \
:
echo "creating new script file." cat <<'EOF' > "$servfile" #!/bin/bash read -p "Please enter a service: " ser servicetest=`getsebool -a | grep ${ser}` if [ $servicetest > /dev/null ]; then echo "we are now going to work with ${ser}" else exit 1 fi EOF
As @BruceK notes, you can prefix your here-doc delimiter with -
(applied to this example: <<-"EOF"
) in order to have leading tabs stripped, allowing for indentation that makes the actual content of the here-doc easier to discern. Note, however, that this only works with actual tab characters, not leading spaces.
Employing this technique combined with the afterthoughts regarding the script's content below, we get (again, note that actual tab chars. must be used to lead each here-doc content line for them to get stripped):
cat <<-'EOF' > "$servfile" #!/bin/bash read -p "Please enter a service name: " ser if [[ -n $(getsebool -a | grep "${ser}") ]]; then echo "We are now going to work with ${ser}." else exit 1 fi EOF
Finally, note that in bash
even normal single- or double-quoted strings can span multiple lines, but you won't get the benefits of tab-stripping or line-block scoping, as everything inside the quotes becomes part of the string.
Thus, note how in the following #!/bin/bash
has to follow the opening '
immediately in order to become the first line of output:
echo '#!/bin/bash read -p "Please enter a service: " ser servicetest=$(getsebool -a | grep "${ser}") if [[ -n $servicetest ]]; then echo "we are now going to work with ${ser}" else exit 1 fi' > "$servfile"
Afterthoughts regarding the contents of your script:
$(...)
is preferred over `...`
for command substitution nowadays.${ser}
in the grep
command, as the command will likely break if the value contains embedded spaces (alternatively, make sure that the valued read contains no spaces or other shell metacharacters).[[ -n $servicetest ]]
to test whether $servicetest
is empty (or perform the command substitution directly inside the conditional) - [[ ... ]]
- the preferred form in bash
- protects you from breaking the conditional if the $servicetest
happens to have embedded spaces; there's NEVER a need to suppress stdout output inside a conditional (whether [ ... ]
or [[ ... ]]
, as no stdout output is passed through; thus, the > /dev/null
is redundant (that said, with a command substitution inside a conditional, stderr output IS passed through).You just need to use single quotes:
$ echo "$TEST" test $ echo '$TEST' $TEST
Inside single quotes special characters are not special any more, they are just normal characters.
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