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

See:  [[BASH:Strings:Find & Replace|Find & Replace]].

----

===== Changing contents within a file =====

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

<WRAP info>
**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.
</WRAP>

----

To change the file in-place:

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

----

===== Put the output of file1 into the pattern space of file2 =====

<file text file1>
aaaaaaaaaaaaaaaaaa //these line go in file2
aaaaaaaaaaaaaaaaaa
aaaaaaaaaaaaaaaaaa
</file>

<file text file2>
Pattern_start
__________ //these are the line to be replaced
__________
Pattern_end
</file>

<code bash>
sed -n '/Pattern_start/,/Pattern_end/{/^Pattern/! d;}" file2 | sed "/Pattern_start/r file1"
</code>

<WRAP info>
**NOTE:**  

  * **<nowiki>/^Pattern/</nowiki>**:  Used this to avoid deleting the **Pattern_start** and **Pattern_end** lines.
</WRAP>

----

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

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