Reversing and trim a String through SHELL script

Shell Programming and Scripting
1

All

  I want to reverse and trim a string using UNIX shell scripts.Iam using Bourne shells.  Can you help me? Thanx in advance

Regards
Deepak

2

Use the search facility.

Here is a result - transposing letters.

It talks about the command rev. It should do the reversing for you.

If rev is not available on your machine try this script below.

[~/temp]$ cat deepak.sh 
#! /bin/sh

# reverse a string

[[ -z "$@" ]] && STR=" a b c d e f g h i j k l m n o p q r s t u v w x y z " || STR="$@"

len=${#STR}

REV=""
for (( i=$len ; i>0 ; i-- ))
do
        REV=$REV""${STR:$i-1:$i}
        STR=${STR%${STR:$i-1:$i}}
done

echo "Reversed string"
echo $REV

[~/temp]$ ./deepak.sh
Reversed string
z y x w v u t s r q p o n m l k j i h g f e d c b a

As for trimming, you can trim the leading and trailing white spaces.

Use this constuct within the script.

# remove leading white spaces
REV=${REV## }
# remove trailing white spaces
REV=${REV%% }

vino

3

All
I want to reverse a string in Korne shells scripting. And Tell me how to convert the below line into korne shells format

for (( i=$len ; i>0 ; i-- ))

Thanx in advance.

Regards
Deepak

4

Looks like you are duplicating this post - Reversing and trim a String through SHELL script .

First question. You have a script that works fine. Why change it for some other shell ? Unless its a homework question. In which case, the rules say

(6) Do not post classroom or homework problems.

Even if you get beyond the if else statement, the construct ${STR:$i-1:$i} is available only for sh. ksh and csh doesnt have this construct documented.

vino

5

DeepakXavier, please do read those rules. You should have posted a followup to your original thread, not start a new thread.

Vino, Linux does not have a Bourne shell. It has bash which is a superset of of the old Bourne shell. Bash is linked to sh for people who use the old Bourne shell. Your script is using bash-only stuff.

For ksh, try...

#! /usr/bin/ksh

str="abcd"
rev=""
typeset -R1 last

while ((${#str})) ; do
        last=$str
        rev=${rev}${last}
        if ((${#str} > 1)) ; then
                typeset -L$((${#str}-1)) rest=$str
                str=$rest
        else
                str=
        fi
done
echo rev = $rev
exit 0
6

to reverse a string - method I

str="program"
echo $str | awk '{
for(i=length($0);i>=1;i--)
printf("%s",substr($0,i,1));
}'

to reverse a string - method II

str="program"
i=${#str}
final=""

while [ $i -gt 0 ]
do
  rev=`echo $str | awk '{printf substr($0, '$i', 1)}'`
  final=$final$rev
  i=$(($i - 1))
done

echo "Reversed String: $final"

to reverse a line

str="this script is to reverse"
i=${#str}
word=""
fin=""
final=""

while [ $i -ge 0 ]
do
temp=`echo $str | awk '{printf substr($0, '$i', 1)}'`
  if [ \( "$temp" = " " \) -o $i -eq 0 ]
  then
     wordlen=${#word}
     while [ $wordlen -gt 0 ]
     do
        revtemp=`echo $word | awk '{printf substr($0, '$wordlen', 1)}'`
        fin=$fin$revtemp
        wordlen=$(($wordlen -1))
     done
     final=$final$fin" "
     fin=""
     word=""
     temp=""
  else
     word=$word$temp
  fi
i=$(($i - 1))
done

echo "Reversed line: $final"