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--- bash:strings:get_a_substring [2021/01/13 22:16] – peter
+++ bash:strings:get_a_substring [2021/01/13 22:56] (current) – peter
@@ Line 1: / Line 1: @@
 ====== BASH - Get a SubString ======
-----
 ===== Format =====
@@ Line 7: / Line 5: @@
 <code bash>
 ${var:start_position:length}
+</code>
+or
+<code bash>
+${var:start_position -length}
+</code>
+or
+<code bash>
+${var: -start_position -length}
+</code>
+or
+<code bash>
+${var: -start_position:length}
 </code>
@@ Line 26: / Line 42: @@
 <WRAP info>
-**NOTE:**  The colon specifies the start position.
+**NOTE:**  A starting position of 0 this means start at the begin; and therefore returns everything.
-Here, 0 means no limit, and returns everything.
 </WRAP>
@@ Line 72: / Line 86: @@
 ----
+===== Return a substring from beginning of a string =====
 <code bash>
@@ Line 88: / Line 104: @@
 **NOTE:**  This starts at position 0; and then returns the next 2 characters.
 </WRAP>
+----
+===== Return last few characters from back of a string =====
+<code bash>
+var="abcdefgh"
+echo ${#var: -4}
+</code>
+returns:
+<code bash>
+efgh
+</code>
+<WRAP info>
+**NOTE:**  This returns the last 4 characters.
+There must be a SPACE before the minus sign!
+Be aware that if the length after the colon is longer than the string, then nothing is returned.
+</WRAP>
+----
+===== Return a substring from back of a string =====
+<code bash>
+var="abcdefgh"
+echo ${#var -1 -3}
+</code>
+returns:
+<code bash>
+efgh
+</code>
+<WRAP info>
+**NOTE:**  This returns the last character; and 3 extra characters.
+There must be a SPACE before the minus signs.
+Be aware that if the length of any position is longer than the string, then nothing is returned.
+</WRAP>
+----
+===== Substrings with Concatenation =====
+<code bash>
+var="abcdefgh"
+echo ${var:0:(-1 -4)}XYZ
+</code>
+returns:
+<code bash>
+abcXYZ
+</code>
 ----