Accessing last x characters of a string in Bash

Question

I found out that with   string 0 3  one can access the first 3 characters of a string  Is there a equivalently easy method to access the last three characters

User · Answer

Another workaround is to use grep -o with a little regex magic to get three chars followed by the end of line     foo 1234567890   echo  foo   grep -o      890   To make it optionally get the 1 to 3 last chars  in case of strings with less than 3 chars  you can use egrep with this regex     echo a   egrep -o    1 3    a   echo ab   egrep -o    1 3    ab   echo abc   egrep -o    1 3    abc   echo abcd   egrep -o    1 3    bcd   You can also use different ranges  such as 5 10 to get the last five to ten chars

User · Answer

Last three characters of string    string  -3   or   string  -3     mind the space between   and -3 in the first form   Please refer to the Shell Parameter Expansion in the reference manual    parameter offset    parameter offset length   Expands to up to length characters of parameter starting at the character specified by offset  If length is omitted  expands to the substring of parameter starting at the character specified by offset  length and offset are arithmetic expressions  see Shell Arithmetic   This is referred to as Substring Expansion   If offset evaluates to a number less than zero  the value is used as an offset from the end of the value of parameter  If length evaluates to a number less than zero  and parameter is not         and not an indexed or associative array  it is interpreted as an offset from the end of the value of parameter rather than a number of characters  and the expansion is the characters between the two offsets  If parameter is          the result is length positional parameters beginning at offset  If parameter is an indexed array name subscripted by         or          the result is the length members of the array beginning with   parameter offset    A negative offset is taken relative to one greater than the maximum index of the specified array  Substring expansion applied to an associative array produces undefined results   Note that a negative offset must be separated from the colon by at least one space to avoid being confused with the     -    expansion  Substring indexing is zero-based unless the positional parameters are used  in which case the indexing starts at 1 by default  If offset is 0  and the positional parameters are used     is prefixed to the list    Since this answer gets a few regular views  let me add a possibility to address John Rix s comment  as he mentions  if your string has length less than 3    string  -3  expands to the empty string  If  in this case  you want the expansion of string  you may use    string    string  lt 3 0 -3   This uses the    ternary if operator  that may be used in Shell Arithmetic  since as documented  the offset is an arithmetic expression  this is valid   Update for a POSIX-compliant solution The previous part gives the best option when using Bash  If you want to target POSIX shells  here s an option  that doesn t use pipes or external tools like cut     New variable with 3 last characters removed prefix   string        The new string is obtained by removing the prefix a from string newstring   string  quot  prefix quot    One of the main things to observe here is the use of quoting for prefix inside the parameter expansion  This is mentioned in the POSIX ref  at the end of the section    The following four varieties of parameter expansion provide for substring processing  In each case  pattern matching notation  see Pattern Matching Notation   rather than regular expression notation  shall be used to evaluate the patterns  If parameter is           or      the result of the expansion is unspecified  If parameter is unset and set -u is in effect  the expansion shall fail  Enclosing the full parameter expansion string in double-quotes shall not cause the following four varieties of pattern characters to be quoted  whereas quoting characters within the braces shall have this effect  In each variety  if word is omitted  the empty pattern shall be used   This is important if your string contains special characters  E g   in dash     string  quot hello ext quot    prefix   string          Without quotes  WRONG    echo  quot   string  prefix  quot   ext     With quotes  CORRECT    echo  quot   string  quot  prefix quot   quot  ext  Of course  this is usable only when then number of characters is known in advance  as you have to hardcode the number of   in the parameter expansion  but when it s the case  it s a good portable solution

User · Answer

You can use tail     foo  1234567890    echo -n  foo   tail -c 3 890   A somewhat roundabout way to get the last three characters would be to say   echo  foo   rev   cut -c1-3   rev

User · Answer

1  Generalized Substring To generalise the question and the answer of gniourf gniourf  as this is what I was searching for   if you want to cut a range of characters from  say  7th from the end to 3rd from the end  you can use this syntax    string  -7 4   Where 4 is the length of course  7-3   2  Alternative using cut In addition  while the solution of gniourf gniourf is obviously the best and neatest  I just wanted to add an alternative solution using cut  echo  string   cut -c       string -2  -  Here     string  is the length of the string  and the  quot - quot  means cut to the end  3  Alternative using awk This solution instead uses the substring function of awk to select a substring which has the syntax substr string  start  length  going to the end if the length is omitted   length  string -2  thus picks up the last three characters  echo  string   awk   print substr  1 length  1 -2

[string] Accessing last x characters of a string in Bash

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