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--- bash:strings:get_a_substring [2021/01/13 22:06] – peter
+++ bash:strings:get_a_substring [2021/01/13 22:56] (current) – peter
@@ Line 1: / Line 1: @@
 ====== BASH - Get a SubString ======
+===== Format =====
+<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>
 ----
-To cut portions of a string:
+===== Return every character =====
 <code bash>
-#!/bin/bash
+var="abcdefgh"
-Str="My name is Peter"
-subStr=${Str:0:6}
+echo ${#var:0}
-echo $subStr
+</code>
+returns:
+<code bash>
+abcdefgh
 </code>
 <WRAP info>
-This script should print out “My nam” as its output.
+**NOTE:**  A starting position of 0 this means start at the begin; and therefore returns everything.
+</WRAP>
-The parameter expansion takes the form ${VAR_NAME:S:L}.
+----
-Here, S denotes starting position and L indicates the length.
+===== Return a substring from a specific position =====
+<code bash>
+var="abcdefgh"
+echo ${#var:3}
+</code>
+returns:
+<code bash>
+defgh
+</code>
+<WRAP info>
+**NOTE:**  This 3 specifies to start from position 3.
 </WRAP>
 ----
-===== Extracting Substrings Using Cut =====
+===== Return a substring between a string =====
-**cut** can be used to ‘cut’ a portion of a string, aka the substring.
+<code bash>
+var="abcdefgh"
+echo ${#var:3:2}
+</code>
+returns:
 <code bash>
-#!/bin/bash
+de
-Str="My name is Peter"
+</code>
-#subStr=${Str:0:6}
-subStr=$(echo $Str| cut -d ' ' -f 1-3)
+<WRAP info>
-echo $subStr
+**NOTE:**  This starts at position 3; and then returns the next 2 characters.
+</WRAP>
+----
+===== Return a substring from beginning of a string =====
+<code bash>
+var="abcdefgh"
+echo ${#var:0:2}
 </code>
+returns:
+<code bash>
+ab
+</code>
+<WRAP info>
+**NOTE:**  This starts at position 0; and then returns the next 2 characters.
+</WRAP>
 ----
-In general to concatenate two variables you can just write them one after another:
+===== Return last few characters from back of a string =====
 <code bash>
-a='Hello'
+var="abcdefgh"
-b='World'
-c="${a} ${b}"
+echo ${#var: -4}
-echo "${c}"
-> Hello World
 </code>
-or
+returns:
 <code bash>
-foo="Hello"
+efgh
-foo="${foo} World"
-echo "${foo}"
-> Hello World
 </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 ${var:0:(-1 -4)}XYZ
+</code>
+returns:
+<code bash>
+abcXYZ
+</code>
+----
+===== Extracting Substrings Using Cut =====
+**cut** can be used to ‘cut’ a portion of a string, aka the substring.
+<code bash>
+#!/bin/bash
+Str="My name is Peter"
+#subStr=${Str:0:6}
+subStr=$(echo $Str| cut -d ' ' -f 1-3)
+echo $subStr
+</code>
+----