[SOLVED] sed copy substring in following line

Issue

I've a .po file I need to copy msgid value into msgstr value if msgstr is empty.

For example

msgid "Hello"
msgstr ""

msgid "Dog"
msgstr "Cane"

Should become

msgid "Hello"
msgstr "Hello"

msgid "Dog"
msgstr "Cane"

Currently, for testing purpose, I'm working with another file, but final script will works inline.

#!/bin/bash
rm it2.po
sed $'s/^msgid.*/&\\\n---&/' it.po > it2.po
sed -i '/^msgstr/d' it2.po
sed -i 's/^---msgid/msgstr/' it2.po

This script has 2 problems (at least):

1. copies msgid into msgstr also when msgstr is not empty;
2. I'm pretty sure that exist a single line or a more elegant solution.

Any help would be appreciated. Thanks in advance.

Solution

You may consider better tool gnu awk instead of sed:

awk -i inplace -v FPAT='"[^"]*"|\\S+' '$id != "" && $1 == "msgstr" && (NF==1 || $2 == "\"\"") {$2=id} $1 == "msgid" {id=$2} 1' file

msgid "Hello"
msgstr "Hello"

msgid "Dog"
msgstr "Cane"

-v FPAT='"[^"]*"|\\S+' makes a quoted string or any non-whitespace field an individual field.

A more readable form:

awk -i inplace -v FPAT='"[^"]*"|\\S+' '
$id != "" && $1 == "msgstr" && (NF==1 || $2 == "\"\"") {$2=id}
$1 == "msgid" {id=$2}
1' file

Answered By - anubhava

Answer Checked By - Timothy Miller (WPSolving Admin)