CODEWITHSUNDEEP
bashscriptingdouble-quotes
mugnozzo
mugnozzo

Reputation: 220

Executing a command (read from an external file) containing Double quoted parameters

Let's say I have a file.txt file like this:

some words
from here
blah blah blah
that begins
this is this

to here
other content

and another file called *config.conf" like this:

name1:value1
name2:value2    
expr:sed -re "s/this/that/g" -ne "/from here/,/to here/ p"
name3:value3
name4:value4

In my script.sh I need to get the whole sed command that is written after "expr:" in the config.conf and execute it in a pipe like this :

#!/bin/bash

pipecommand=$(cat info | grep -e "^expr:" | sed -re "s/^expr://g")
cat file.txt | $pipecommand > output.file

but I get this error:

sed: -e expression #1, char 1: unknown command: `"'

I've read about many similar questions here and the solution was using an array like this:

pipecommand=($(cat info | grep -e "^expr:" | sed -re "s/^expr://g"))
cat file.txt | ${pipecommand[@]} > output.file

Unfortunately this works only with less complex commands and only if I assign the "sed...blah blah blah" command directly to the variable, without reading it from a file.

Do some of you know a working solution to this?

P.S.: I can change both the script.sh and the config.conf files.

Upvotes: 2

Views: 388

Answers (3)

Charles Duffy
Charles Duffy

Reputation: 295490

Interpreting this as a question about how to apply the advice from Reading quoted/escaped arguments correctly from a string to your use case:

#!/usr/bin/env bash

# the sed expression here is modified to work with BSD sed, not only GNU sed
pipecommand=$(sed -ne 's/^expr://p' <info)

array=( )
while IFS= read -r -d ''; do
  array+=( "$REPLY" )
done < <(xargs printf '%s\0' <<<"$pipecommand")

<file.txt "${array[@]}" > output.file

This safer than eval, insofar as the words inside your expr: can be treated only as literal arguments, and can't be parsed as redirections, substitutions, parameter expansions, or other shell syntax. Of course, an expr of sh -c '...' can be used to enable shell syntax inside the ... section: Constraining the command (the first element of the array) is necessary if you genuinely wanted to sandbox, control or constrain the invoked command.

Upvotes: 3

chepner
chepner

Reputation: 531325

Turn your config file into a plugin with a well-defined interface. Here, your script expects a function named sed_wrapper, so you provide a definition with that name in your "config file" (renamed to lib.sh here).

# This is lib.sh
sed_wrapper () {
    sed -re "s/this/that/g" -ne "/from here/,/to here/ p"
}

Then, in your script, call the named function.

. lib.sh

sed_wrapper < file.txt > output.file

Upvotes: 2

KamilCuk
KamilCuk

Reputation: 141155

Sadly, you need eval.

pipecommand=$(grep "^expr:" info | cut -d: -f2-)
eval "$pipecommand" <file.txt > output.file

Try to avoid eval.

Upvotes: 2

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