Table of Contents

BASH - Files - Find & Replace a String within a File

See: Find & Replace.

Changing contents within a file

contents=$(< infile.txt)
$ echo "${contents/$old/$new}"

NOTE: This reads the file into a Bash variable and uses parameter expansion.

  • infile.txt: The input file here is named infile.txt.
  • $old: The string to replace.
  • $new: The replacement string.

To change the file in-place: 

echo "${contents/$old/$new}" > infile.tmp && mv infile.tmp infile.txt

Put the output of file1 into the pattern space of file2

file1
aaaaaaaaaaaaaaaaaa //these line go in file2
aaaaaaaaaaaaaaaaaa
aaaaaaaaaaaaaaaaaa
file2
Pattern_start
__________ //these are the line to be replaced
__________
Pattern_end
sed -n '/Pattern_start/,/Pattern_end/{/^Pattern/! d;}" file2 | sed "/Pattern_start/r file1"

NOTE:

  • /^Pattern/: Used this to avoid deleting the Pattern_start and Pattern_end lines.

If the lines between Pattern_start and Pattern_end contain only hyphens then you can use this: 

sed -n '/Pattern_start/,/Pattern_end/{/^---*/d;}" file2 | sed "/Pattern_start/r file1"