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--- bash:files:find_replace_a_string_within_a_file [2021/02/10 16:05] – created peter
+++ bash:files:find_replace_a_string_within_a_file [2021/02/10 16:14] (current) – [Put the output of file f1 into the pattern space of file f2] peter
@@ Line 1: / Line 1: @@
 ====== 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>