CODEWITHSUNDEEP
regexbash
Calaf
Calaf

Reputation: 10817

Making quotation marks survive to a command run inside a bash script

The following code saves my_string in the file my_filename and then checks whether pattern1 and pattern2 are in the file. The first is; the second isn't.

#!/bin/bash

my_string="One two three four" 
pattern1="two three"
pattern2="two four"

my_filename="my_temp_file"

safeGrepCommand() {
    typeset command_to_run="$*"
    typeset ret_code

    # echo command_to_run=$command_to_run
    eval $command_to_run
    ret_code=$?
    if [ $ret_code != 0 ]; then
        printf "Pattern %s is not in the file %s.\n" "${my_pattern}" "${my_filename}"
        exit $ret_code
    fi
}

echo $my_string > $my_filename

grep_command1="grep --quiet ${pattern1} ${my_filename}"
safeGrepCommand "$grep_command1"

grep_command2="grep --quiet ${pattern2} ${my_filename}"
safeGrepCommand "$grep_command2"

rm -f $my_filename

I am expecting to see the output

Pattern two four is not in the file my_temp_file.

Instead I see

grep: three: No such file or directory
grep: four: No such file or directory

As you'll see if you uncomment the echo line inside the function, the problem is that the quotation marks are not seen by grep.

command_to_run=grep --quiet two three my_temp_file
command_to_run=grep --quiet two four my_temp_file

How do I get bash to pass the quotation marks to grep? Alternatively, how do I specify "two three" as a regexp with [:space] and not worry about quotation marks.

Upvotes: 0

Views: 85

Answers (2)

rici
rici

Reputation: 241701

Here's one way of resending arguments in a shell function:

doit_or_complain() {
  # The arguments are captured only to show how to do it. In practice,
  # I would just use "${@}" to run the command.
  local -a command=("$@")
  "${command[@]}"
  local rc=$?
  if ((rc)); then
    echo "The command failed" >> /dev/stderr
  fi
  return $rc
}

That will work with any random arguments:

doit_or_complain grep "a  b" "./my file with spaces in its name"

If you want to pass a complicated command to the shell function, you should use an array:

theCommand=(grep "a  b" "./my file with spaces in its name")
#...
doit_or_complain "${theCommand[@]}"

Note: The function in the OP used exit $rc if the command failed. That will exit the current shell, not just the function, which might be considered a tad unexpected, if not unsafe.

Upvotes: 1

nu11p01n73R
nu11p01n73R

Reputation: 26667

Wrap the pattern variable in double quotes as

grep_command1="grep --quiet \"${pattern1}\" \"${my_filename}\""
safeGrepCommand "$grep_command1"

grep_command2="grep --quiet \"${pattern2}\" \"${my_filename}\""
safeGrepCommand "$grep_command2"

Upvotes: 0

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