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I want to replace a sed patter match by it's ascii decimal representation as a comma-separated list. The transformation of the patter into the csv-integer sting in done inside a bash function. The function is doing its job but I struggle to integrate it into the sed call. Here is the example code:

#!/bin/bash
xx(){
##turns a string into its
##ascii-integer representation as a comma-separated list
##ignores double quotes at the start and end
    n=0;o=""
    for((k=1;k<$(echo $1 | wc -c);k++))
    do
    x=$(echo $1 | cut -b"$k")
    a=$(printf '%d\n' "'$x" )
    if [ $a = 34 ]
    then
        continue
    else
        n=$(($n+1))
        if [ $n = 1 ]
        then
        o=$a
        else
        o=$(echo $o","$a)
        fi
    fi
    done
    o=$(echo '('$o')')
    echo $o
}
##this works
xx "\"bla\""
##this does not work
y=$(echo "\"bla_x\"" | sed -e "s/bla/$(xx &)p")

The function works but the sed integration fails. From googling I got the impression that this should be in principle possible, so there might be just a small syntax mistake.

Any help much appreciated.

All the best

NB: in the final application the input to sed is a file with reg-exp patterns (e.g. "k_[[:alnum:]]{5}") to be replaced by the csv-concatenation. So eventually "xx" must bu called out of sed.

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2 Answers 2

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3

Look closely at your sed invocation, it is missing the closing slash of s/// command. Next, you are using double quotes, so even before sed runs, the rhs of the s/// command has been filled in due to double quote interpolation. Which is not what you want. However, this still won't get you past the goalpost though.

There is a little-known flag /e in the GNU sed's s/// command. This is exactly what the doctor ordered in this case. What it does is, dynamically construct the rhs of the s/// command based on running the shell code given in the rhs and replacing it with it's output. Note: It requires the whole of the pattern space be matched.

This also requires that your user defined function be exported to be available to the children.

#this does not work
##this is what YOU wrote 
y=$(echo "\"bla_x\"" |
sed -e "s/bla/$(xx &)p")

##this now WORKS
export -f xx
y=$(
echo '"bla_x"' |
sed -Ee '
  s/^.(.*)(_x).$/echo "$(xx '"\1"')\2"/e
'
)
echo "$y"
(98,108,97)_x

Note the use of single quotes in the sed command.

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  • Thanks, but doesn't work at my side. I don't know why you have a curled parenthesis in the string, maybe its a typo. However, after removing it I get the message sh: line 1: xx: command not found Commented Jan 28, 2021 at 9:43
  • You need to export the function xx for it to be visible iin the child process inside sed /e command. I have added the export line. Commented Jan 28, 2021 at 11:04
  • Thanks. indeed now it works. ............ However, as you pointed out "the whole pattern space must be matched" which basically gives the wrong output. That is, for the example "bla_x" should come out as "(98,108,97)_x". Any idea? Commented Jan 28, 2021 at 14:37
  • See my edits to see the expected output Commented Jan 28, 2021 at 14:57
1

If I understand you correctly, you can simplify your function using printf:

xx() {
  # create an array to store every character of the word
  declare -a arr

  # loop the word to every char, removing quotes
  for i in $(echo "${1//\"}" | grep -o .); do 
    # store the ascii value
    arr+=($(printf "%d" "'$i"))
  done 

  # create a variable with the values, comma separated
  printf -v ascii "%s," "${arr[@]}" 

  # print the result adding the parenthesis and removing the last comma
  echo "(${ascii%,})"
}

$ xx "\"bla\""
(98,108,97)

Now, xx removes the double quotes, but in your sed command you are trying to send a quoteless pattern (bla, not "bla"), so if you don't want them in the output of the next code, you have to remove them some other way:

p=bla
s="\"bla_x\""
c=$(xx "$p")

$ echo "$s" | sed "s/$p/$c/"
"(98,108,97)_x"
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  • Hi. Thanks for the improvement of "xx". However, for the rest it wont work because eventually the input to sed will be a file which contains patterns which must be replaced by the integer csv-concatenation. That means that "xx" must be called out of sed directly. Commented Jan 28, 2021 at 4:35
  • @user1407220 Could you add this information to your question? It's important so future users can give better answers, or I to change mine. Commented Jan 28, 2021 at 4:38
  • sure. no worries. Commented Jan 28, 2021 at 4:55

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