Replace newline if condition is met in next line in text file with linux command line tools

user_18749361 0
Viewed 96

Input

$ cat input.txt
345 "cuad"  "dfr"
23  "test3" "dfec2
"v1"
33 v2
v3"
32  "key3"  "fer"
12  "rte"   "ef"

Goal, I would like to replace the newline with a space only if the next line not starts with number and tab

345 "cuad"  "dfr"
23  "test3" "dfec2 "v1" 33 v2 v3"
32  "key3"  "fer"
12  "rte"   "ef"

trying this bash command to remove new lines if condition on the next line is met but I can't adapt it to my needs

Attempt, it doesn't work

$ perl -0777 -pe 's/\n(?=[^0-9]+\t)/ /g' input.txt
perl bash regex
3 Answers

You may use this perl command with a negative lookahead:

perl -0777 -pe 's/\R(?!\d+\t|\Z)/ /g' file

345 "cuad"  "dfr"
23  "test3" "dfec2 "v1" 33 v2 v3"
32  "key3"  "fer"
12  "rte"   "ef"

RegEx Details:

  • \R: Match any line break character (unicode compliant)
  • (?!\d+\t|\Z): Negative lookahead to assert that we don't have 1+ digits followed by a tab OR end of input ahead
user_5482250

Without slurping:

perl -pe'
   chomp;
   if ( /^\d+\t/ ) {
      print "\n" if $. > 1;
   } else {
      print "\t";
   }
   END { print "\n" if $. > 0; }
'
user_5899240

As an alternative in GNU sed:

sed ':a; N; /\n[0-9][0-9]*\t/{P;D;}; s/\n/ /; ba' file

Please note that this command is specific to GNU sed.

user_138090010
Related