Question

ksh - substr function

Asked by: mliberi

Is it possible to extract a substring from a string using ksh INTERNAL ONLY functions?

I know the task could be easily done by forking a 'cut' or 'awk' and probably many others, but it is not efficient.

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Asked On
1999-02-18 at 05:58:59ID10129947
Tags

ksh

,

substring

Topic

Unix Systems Programming

Participating Experts
4
Points
50
Comments
9

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Answers

 

by: ozoPosted on 1999-02-18 at 08:20:16ID: 1296656

STRING=12345678
STRING=${STRING#???}
STRING=${STRING%??}
echo $STRING

 

by: prakashkPosted on 1999-02-18 at 09:07:01ID: 1296657

Here's the substr function which does what you want:

#############################################################
# Usage: substr string [offset [length]]
# offset values start from 0 (that is, first character has offset 0)

substr()
{
        typeset _str="$1"
        typeset -i _strlen=${#_str}

        typeset -i _offset="${2:-0}"
        typeset -i _sublen="${3}"

        typeset -i _rlen
        ((_rlen=_strlen-_offset))

        typeset -R${_rlen} _substr=${_str}
        typeset -L${_sublen} _substr=${_substr}

        echo $_substr
}
#############################################################

$ substr 1234567890 3 4
4567
$ substr 1234567890 3
4567890
$ substr 1234567890 0 10
1234567890

One caveat, though: It doesn't work if your string contains leading or trailing blanks.

 

by: ahoffmannPosted on 1999-02-18 at 10:21:05ID: 1296658

see ozo's comment, then check man-page for Variable Substitution, there are much more such things:
${var:-word}
${var-word}
${var:=word}
${var=word}
${var:?word}
${var?word}
${var:+word}
${var+word}
${var##word}
${var#word}
${var%%word}
${var%word}

 

by: ahoffmannPosted on 1999-02-18 at 10:21:11ID: 1296659

see ozo's comment, then check man-page for Variable Substitution, there are much more such things:
${var:-word}
${var-word}
${var:=word}
${var=word}
${var:?word}
${var?word}
${var:+word}
${var+word}
${var##word}
${var#word}
${var%%word}
${var%word}

 

by: mliberiPosted on 1999-02-19 at 02:46:14ID: 1296660

Thank you all.

I can't grade prakashk answer because the function must work with ANY input string, so the limitation "no blanks" isn't acceptable.
I already wrote something like that but I don't want to worry about blanks and I was searching for something better.

Starting from ozo's key comment I developed the following:

function strrep
# $1 string
# $2 number of repetitions
{
  typeset -i rcl=$2 l=0
  while ((l<rcl))
  do
    let l+=1
    echo "$1\c"
  done
}

function substr
# $1 string
# $2 offset
# $3 len
{
  typeset rc=${1#$(strrep "?" $2)}
  rc=${rc%$(strrep "?" $((${#rc}-$3)))}
  echo "$rc\c"
}

that definitively solves the problem.

To ozo: please lock the question, I'm going to grade 'B' your comment.

 

by: ozoPosted on 1999-02-19 at 03:42:58ID: 1296661

Since I didn't build a function for you, how about 35 points of 'A' instead of 50 points of 'B'?

 

by: mliberiPosted on 1999-02-19 at 05:56:09ID: 1296662

ozo, I'm not sure to well understand your question.

How may I decrease the number of points from 50 to 35?
Why do you prefer 35*4 instead of 50*3?

 

by: elfiePosted on 1999-02-23 at 02:08:09ID: 1296663

ozo doesn't want the point, he wants a-grades
(correct me if wrong)

 

by: ozoPosted on 1999-04-12 at 03:26:08ID: 1296664

Sorry, I forgot this was open.

20120131-EE-VQP-002

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