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BASH - Get a SubString

Format

${var:start_position:length}

or

${var:start_position -length}

or

${var: -start_position -length}

or

${var: -start_position:length}

var="abcdefgh"
 
echo ${#var:0}

returns:

abcdefgh

NOTE: The number after the colon specifies the start position.

At starting position is 0 this means start at the begin; and therefore returns everything.

var="abcdefgh"
 
echo ${#var:3}

returns:

defgh

NOTE: This 3 specifies to start from position 3.

var="abcdefgh"
 
echo ${#var:3:2}

returns:

de

NOTE: This starts at position 3; and then returns the next 2 characters.

var="abcdefgh"
 
echo ${#var:0:2}

returns:

ab

NOTE: This starts at position 0; and then returns the next 2 characters.

var="abcdefgh"
 
echo ${#var: -4}

returns:

efgh

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.

var="abcdefgh"
 
echo ${#var -1 -3}

returns:

efgh

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.

cut can be used to ‘cut’ a portion of a string, aka the substring.

#!/bin/bash
Str="My name is Peter"
#subStr=${Str:0:6}
 
subStr=$(echo $Str| cut -d ' ' -f 1-3)
echo $subStr