Programming Forums > Script Programming > Sed and Awk

jim mcnamara · Aug 16th, 2006, 4:50 PM

This forum is near death. Maybe some interesting activity will restore it to life.

Challenge - write a simple sed script to reverse a string or file:

(Toggle Plain Text)

prompt$> echo "hi there" | sed 'your script goes here'
ereht ih

ie. the behavior should match the rev command utility. I'll post an answer
on Friday....

Infinite Recursion · Aug 16th, 2006, 8:43 PM

I'd like to see more entries in this section also... maybe a weekly script challenge or something.

(Toggle Plain Text)

#!/usr/bin/sed -f

# reverse all chars of each line, keep line ordering

# ignore empty lines, i.e. nothing to reverse
/./!b

# escape ! by doubling it, place markers at beginning and end of line
# the markers are -!- which can never happen after the escaping of !
s/!/!!/g
s/^/-!-/
s/$/-!-/

# swaps first char after first maker, with first char before last marker
# and then advance the markers through the swapped chars
ta
:a
s/-!-\([^!]\|!!\)\(.*\)\([^!]\|!!\)-!-/\3-!-\2-!-\1/
ta

# delete markers, and then unescape the !s
s/-!-//g
s/!!/!/g

ir@grendel [~/code/sed]# echo "hi there" | ./s.sh
ereht ih

jim mcnamara · Aug 17th, 2006, 8:46 AM

I came up with:

(Toggle Plain Text)

sed '/\n/!G;s/\(.\)\(.*\n\)/&\2\1/;//D;s/.//'

Celsoft · Aug 27th, 2008, 6:30 AM

Simple -

echo ereht ih

next challAnge ...

L7Sqr · Aug 27th, 2008, 7:14 AM

Somehow 'echo' doesnt seem quite like a sed script. Although, I have been known to overlook the obvious before...

Jimbo · Aug 27th, 2008, 10:40 AM

Quote:

Originally Posted by Celsoft

Simple -

echo ereht ih

next challAnge ...

You're overlooking the obvious and the subtle. Obvious: your script should reverse any input string or file. Subtle: the thread has been dead for 2 years.

Aug 16th, 2006, 4:50 PM	#1
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	sed challange This forum is near death. Maybe some interesting activity will restore it to life. Challenge - write a simple sed script to reverse a string or file: (Toggle Plain Text) prompt$> echo "hi there" \| sed 'your script goes here' ereht ih prompt$> echo "hi there" \| sed 'your script goes here' ereht ih ie. the behavior should match the rev command utility. I'll post an answer on Friday....

Aug 16th, 2006, 8:43 PM	#2
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	I'd like to see more entries in this section also... maybe a weekly script challenge or something. (Toggle Plain Text) #!/usr/bin/sed -f # reverse all chars of each line, keep line ordering # ignore empty lines, i.e. nothing to reverse /./!b # escape ! by doubling it, place markers at beginning and end of line # the markers are -!- which can never happen after the escaping of ! s/!/!!/g s/^/-!-/ s/$/-!-/ # swaps first char after first maker, with first char before last marker # and then advance the markers through the swapped chars ta :a s/-!-\([^!]\\|!!\)\(.\)\([^!]\\|!!\)-!-/\3-!-\2-!-\1/ ta # delete markers, and then unescape the !s s/-!-//g s/!!/!/g #!/usr/bin/sed -f # reverse all chars of each line, keep line ordering # ignore empty lines, i.e. nothing to reverse /./!b # escape ! by doubling it, place markers at beginning and end of line # the markers are -!- which can never happen after the escaping of ! s/!/!!/g s/^/-!-/ s/$/-!-/ # swaps first char after first maker, with first char before last marker # and then advance the markers through the swapped chars ta :a s/-!-\([^!]\\|!!\)\(.\)\([^!]\\|!!\)-!-/\3-!-\2-!-\1/ ta # delete markers, and then unescape the !s s/-!-//g s/!!/!/g ir@grendel [~/code/sed]# echo "hi there" \| ./s.sh ereht ih __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Aug 17th, 2006, 8:46 AM	#3
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	I came up with: (Toggle Plain Text) sed '/\n/!G;s/\(.\)\(.\n\)/&\2\1/;//D;s/.//' sed '/\n/!G;s/\(.\)\(.\n\)/&\2\1/;//D;s/.//'

Aug 27th, 2008, 6:30 AM	#4
Celsoft Newbie Join Date: Aug 2008 Posts: 3 Rep Power: 0	Re: sed challange Simple - echo ereht ih next challAnge ...

Aug 27th, 2008, 7:14 AM	#5
L7Sqr Hobbyist Programmer Join Date: Jun 2005 Location: here Posts: 137 Rep Power: 0	Re: sed challange Somehow 'echo' doesnt seem quite like a sed script. Although, I have been known to overlook the obvious before... __________________ "...and though our kids are blessed their parents let them shoulder all the blame." - The Quiet Things That No One Ever Knows [BrandNew]

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