I have a script wherein you have to input a string with a length greater then or equal to 1 and less then 26.
If that's not the case I want to return an error. But that's the part I have figured out
lengthAlphabetInput=${#1}
if [ $lengthAlphabetInput -lt 1 ] || [ $lengthAlphabetInput -gt 26 ]
then
echo "error: key needs to be between 1 and 26 characters"
exit 1
fi
Other than that I would like to check if the input the user gave is a permutation of (a part of) the alphabet.
For example if the user inputs "abc" I want to return an error "abc is
not a permutation of the alphabet"
if the user inputs "xxxgsdnoip" I again want to return the same error
because I don't want the user to use the same letter more than once.
But the input "xyz" or "jhcwslaedmviotrgzxkbynpuqf" would be correct
because these are permutations of the alphabet. (x instead of a, y
instead of b and z instead of c).
Can anyone help me transform this idea into code?
I realized that this is a question raised by a student, so I did not write down a detailed answer, since the experience of reading manual and figuring it out yourself will really help you learn how to use bash (actually the GNU/BSD core utilities), as said by #binaryzebra. What you should do is:
Learn to read manual in bash, with command man, such as man sort for the manual of sort utility. Hit Up/Down arrow key or PageUp/PageDown key to scroll; hit q to exit. Reading manual is your first step into Unix world. Sure you can skip this and find all the information from Google, but learning to read manual will do you more good in the long run.
Read the manual of sed and learn substitution with regular expression. The manual is a little too long for a newcomer, but luckily you do not need to read it all; just scan the manual and find the part about substitution; read the examples as well, if there is any. Practice with some test file. Now you know how to check whether input contains only letters (instead of whitespace, symbols, etc.), as well as how to split each character in its own line.
Read the manual of uniq. It has a much shorter manual; reading the whole manual won't take long.
Now learn the pipeline feature in bash. I cannot find a short and focused manual entry, so you may as well just read the online manual from GNU. With the help of pipeline, you can combine sed and uniq to detect duplicated characters.
By "permutation", it seems that you do not want the characters in their original order. If so, read the manual of the sort utility and think how it can help you.
You do not seem to care about whether all 26 letters are there. If this is the case, you probably do not need the wc (word count) utility, unless you require the subset of letters be continuous (such as "cdefg" instead of "cdhjk").
That's all the hints; good luck with your homework.
#!/usr/bin/perl
$_=shift;
print "not ok:repeated: $1\n" if/(.).*\1/;
my $i=0;
my #s= ( map { ord($_)-97 != $i++ ? ():($_)} split(''));
print "not ok:samePlace: #s\n" if #s;
usage:
$ perl ex.pl rty
$ perl ex.pl abc
not ok:samePlace: a b c
$ perl ex.pl ddss
not ok:repeated: d
Related
My intent is to capture the values of a string that I type and have those values be shifted to other letters. Essentially it would be a fake translation program or custom cipher generation script. Example of function:
I would type the sentence:
Who are you?
and the output would be shifted by lets say 1 to the next consonant or vowel, for example. The script would also need to know how to skip vowels or consonants as needed, and for the sake of argument y would always be considered a vowel. So the output would be:
Xju eso auy?
This is something I wanted to attempt for a creative writing project as a means of making another language. Ideally the shift variable could be an input as well to work with to find the best outcome. Possibly even variable shifts for vowels and consonants at the same time?
If you truly are doing this for a creative writing project, then I submit that diving deep into the programming is not warranted. None of the input transformations you described require decisions to be made by the program. That is; once an encoding is chosen, the incoming letters will be each be firmly associated with outgoing letters. This greatly expands your options for how to achieve this, and greatly simplifies the complexity of the task.
Since you tagged Terminal, here are a couple commands you could use in action:
echo "Who are you?" | perl -pe 'tr/N-ZA-Mn-za-m/A-Za-z/'
outputs: Jub ner lbh?
This is the famous Rot13 "encoding" (all it does is substitute the letter that is 13 later in the alphabet). It's particularly handy as 13 is half the alphabet's 26, so putting some "encoded" text in will give you back the original text:
echo "Jub ner lbh?" | perl -pe 'tr/N-ZA-Mn-za-m/A-Za-z/'
outputs: Who are you?
echo just sends text to the screen or other commands. Here we echo our text "How are you?" into a pipe | to pass it to the next command perl, which is a very powerful and flexible text-manipulation and reporting program. The rest of the line is just instructions for perl on how to spin 13 letters later in the alphabet.
Quick note; normally hitting return runs the command in terminal. You can put a backslash \ at the end of a line though and hit return, it will then let you keep typing on the next line but treat it all as one command. Handy for lining things up.
echo "How are you?" | tr \
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz' \
'DFVBTXEUWZOSHCJMAQYRINKLPGdfvbtxeuwzoshcjmaqyrinklpg'
outputs: Ujk dqt pji?
There's another command, tr. This example demonstrates an arbitrary substitution—in this case, random. It looks through that first long set of letters, and swaps in instead the letter in the second long set that is in the matching position. Since this substitution example is random, you could use this kind of mapping to create "Cryptogram" puzzles.
The great thing about the tr command is that you can tell it to use whatever input-to-output "mapping" you'd like. Sure, it's a bit manual, but hey—no programming needed!
Here's the mapping to achieve your requested "consonants and vowels" example shift:
echo "Who are you?" | tr \
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz' \
'ECDFIGHJOKLMNPUQRSTVYWXZABecdfighjoklmnpuqrstvywxzab'
Outputs: Xju esi auy? Not doing it by hand has its advantages—you missed a vowel in there.
So if you need to rapidly try different mappings, consider learning a bit more about perl (or simpler: sed. or more complex: awk. Or or or…). If, instead, you don't mind a bit of careful command-construction, just lining up each incoming letter with your desired output letter, I think tr would serve nicely.
In unix scripting
I have a file which has lines as follows:
if(a==b || b=c && c==d)
if(a!=b)
if(a=b)
i have to print only those lines which is having assignment operator i.e
if(a==b || b=c && c==d) and
if(a=b)
Anybody pls Help
So what you're looking for is (simplistically) an = on its own, with no other = abutting it. This can be done with the regex [^=]=[^=] (an = with something other than = on both sides).
Unfortunately, that will also capture things like != or >= so you may want to expand it a bit. As a start:
grep '[^!<>=]=[^=]' inputFile
That should catch the vast majority although you're in the same boat as those who want to process XML with regexes rather than an XML processor - there will probably always be some edge case that you don't get simply because regex is a far simpler tool than a language parser. However, as stated, it should be fine for all but the weirdest of edge cases.
And you may still have to handle cases where (for example) the = may be at the start or end of the line but this would be pretty unlikely since any coder formatting their code like that is clearly insane :-)
The following should be a decent approximation with GNU grep:
grep -E '([[:alnum:]]|[[:space:]]|^)=([[:alnum:]]|[[:space:]]|$)'
This will show = delimited by alpha-numeric and whitespaces. It won't find = delimited by punctuation (e.g (=)) - we can't just add [[:punct:]] to the character classes (or just replace them with [[:print:]]) because that would include == and !=. It's possible to manually specify punctuation apart from = and ! if you want.
I came across a question in my interview
Shell script to show frequency of each word in file and in a directory
A
- A1
- File1.txt
- File2.txt
-A2
- FileA21.txt
-A3
- FileA31.txt
- FileA32.txt
B
-B1
- FileB11.txt
- FileB12.txt
- FileB13.txt
-B2
-FileB21.txt
I believe that I understood the question by understanding that Directories A and B are two separate directories with A1, A2 & A3 being sub-directories of A, and B1 and B2 being sub-directories of B. So I answered like this.
Find . ‘\(-name “A” –and –name “B”\)’ –type f –exec cat ‘{}’ \; | awk ‘{c[$1]++} END {for (i in c) print i, c[i]}’
But still I got an feedback that the above script was not good enough. What's wrong in the given script?
The major limitation is that the script assumes there is exactly one word per line. c[$1]++ just increments the occurrence of the first field of each line.
The question didn't mention anything about the number of words in a line, so I'd assume this wasn't the intention - you need to go through each word in a line. Also, what about empty lines? With an empty line, $1 will be the empty string, so your script will end up counting "empty" words (which it will happily show as part of the output).
In awk, the number of fields in a line is stored in the built-in variable NF; thus it is easy to write code to loop through the words and increment the corresponding count (and it has the nice side effect of implicitly ignoring lines without words).
So, I would do something like this instead:
find . -type f -exec cat '{}' \; | awk '{ for (i = 1; i <= NF; i++) w[$i]++ } END { for (i in w) printf("%-10s %10d\n", i, w[i]) }'
I removed the directory names constraints in the argument to find(1) for the sake of conciseness, and to make it more general.
This is (probably) the main issue with your solution, but the question is (intentionally) vague and there are many things left to discuss:
Is it case-sensitive? This solution treats World and world as different words. Is this desired?
What about punctuation? Should hello and hello! be treated as the same word? What about commas? That is, do we need to parse and ignore punctuation?
Speaking of which - what about things like what's vs. what? Do we consider them different words? And it's vs. its? English is tricky!
Most important of all (and related to the points above), what exactly defines a word? We assumed a word is a sequence of non-blanks (the default in awk). Is this accurate?
If there are no words in the input, what do we do? This solution prints nothing - maybe we should print a warning message?
Is there a fixed number of words in a line? Or is it arbitrary? (E.g. if there's exactly one word per line, your solution would be enough)
FWIW, always remember that your success in an interview is not a binary yes/no. It's not like: Oops, you can't do X, so I'm going to reject you. Or: Oops, wrong answer, you're out. More important than the answer is the process that gets you there, and whether or not you are aware of (a) the assumptions you made; and (b) your solution's limitations. The questions above show ability to consider edge cases, ability to clarify assumptions and requirements, etc, which is way more important than getting the "right" script (and probably there's no such thing as The Right Script).
Hi I am writing a bash script and I have a string
foo=1.0.3
What I want to do is examine the '3'. The first thing I did was get rid of the periods by doing this. bar=echo $foo|tr '.' ' ' with backticks around echo until the last single quote (not sure how to accomplish writing that.
When I do an echo $bar it prints 1 0 3. Now how do I create a variable that holds only the 3? thank you very much
As you are no doubt learning about bash, there are many many ways to achieve your goals. I think #Mat's answer using bar=${foo##*.} is the best so far, although he doesn't explain how or why it works. I strongly recommend you check out the bash tutorial on tldp, it is my goto source when I have questions like this. For string manipulation, there is a section there that discusses many of the different ways to go about this sort of thing.
For example, if you know that foo is always going to be 5 characters long, you can simply take the fifth character from it:
bar=${foo:4}
That is, make bar the fifth position of foo (remember, we start counting from zero, not from one).
If you know it is always going to be the last position of foo, then you can just count backwards:
bar=${foo: -1}
Notice there is a space between the -1 and the colon, you need that (or parenthesis) to escape the negative sign.
To explain #Mat's answer, I had to look at the link I provided above. Apparently the double pound signs (hash mark, octothorpe, whatever you want to call them) in the expression:
${string##substring}
Mean to delete longest match of $substring from front of $string. So you are looking for the longest match of *. which equates to everything before a dot. Pretty cool, huh?
This should work:
bar=$(echo $foo|cut -d. -f3)
If you know you only want the part after the last dot (not the third item in a .-separated list) you can also do this:
bar=${foo##*.}
Advantage: no extra process or subshell started.
One way: Build an array and take position 2:
array=(`echo $foo | tr . ' '`)
echo ${array[2]}
This should also work too:
echo $foo | awk -F. '{print $3}'
Ok,first post..
So I have this assignment to decrypt cryptograms by hand,but I also wanted to automate the process a little if not all at least a few parts,so i browsed around and found some sed and awk one liners to do some things I wanted done,but not all i wanted/needed.
There are some websites that sort of do what I want, but I really want to just do it in bash for some reason,just because I want to understand it better and such :)
The script would take a filename as parameter and output another file such as solution$1 when done.
if [ -e "$PWD/$1" ]; then
echo "$1 exists"
else
echo "$1 doesnt exists"
fi
Would start the script to see if the file in param exists..
Then I found this one liner
sed -e "s/./\0\n/g" $1 | while read c;do echo -n "$c" ; done
Which works fine but I would need to have the number of occurences per letter, I really don't see how to do that.
Here is what I'm trying to achieve more or less http://25yearsofprogramming.com/fun/ciphers.htm for the counting unique letter occurences and such.
I then need to put all letters in lowercase.
After this I see the script doing theses things..
-a subscript that scans a dictionary file for certain pattern and size of words
the bigger words the better.
For example: let's say the solution is the word "apparel" and the crypted word is "zxxzgvk"
is there a regex way to express the pattern that compares those two words and lists the word "apparel" in a dictionnary file because "appa" and "zxxz" are similar patterns and "zxxzgvk" is of similar length with "apparel"
Can this be part done and is it realistic to view the problem like this or is this just far fetched ?
Another subscript who takes the found letters from the previous output word and that swap
letters in the cryptogram.
The swapped letters will be in uppercase to differentiate them over time.
I'll have to figure out then how to proceed to maybe rescan the new found words to see if they're found in a dictionnary file partly or fully as well,then swap more letters or not.
Did anyone see this problem in the past and tried to solve it with the patterns in words
like i described it,or is this just too complex ?
Should I log any of the swaps ?
Maybe just scan through all the crypted words and swap as I go along then do another sweep
with having for constraint in the first sweep to not change uppercase letters(actually to use them as more precise patterns..!)
Anyone did some similar script/program in another langage? If so which one? Maybe I can relate somehow :)
Maybe we can use your insight as to how you thought out your code.
I will happily include the cryptograms I have decoded and the one I have yet to decode :)
Again, the focus of my assignment is not to do this script but just to resolve the cryptograms. But doing scripts or at least trying to see how I would do this script does help me understand a little more how to think in terms of code. Feel free to point me in the right directions!
The cryptogram itself is based on simple alphabetic substitution.
I have done a pastebin here with the code to be :) http://pastebin.com/UEQDsbPk
In pseudocode the way I see it is :
call program with an input filename in param and optionally a second filename(dictionary)
verify the input file exists and isnt empty
read the file's content and echo it on screen
transform to lowercase
scan through the text and count the amount of each letter to do a frequency analysis
ask the user what langage is the text supposed to be (english default)
use the response to specify which letter frequencies to use as a baseline
swap letters corresponding to the frequency analysis in uppercase..
print the changed document on screen
ask the user to swap letters in the crypted text
if user had given a dictionary file as the second argument
then scan the cipher for words and find the bigger words
find words with a similar pattern (some letters repeating letters) in the dictionary file
list on screen the results if any
offer to swap the letters corresponding in the cipher
print modified cipher on screen
ask again to swap letters or find more similar words
More or less it the way I see the script structured.
Do you see anything that I should add,did i miss something?
I hope this revised version is more clear for everyone!
Tl,dr to be frank. To the only question i've found - the answer is yes:) Please split it to smaller tasks and we'll be happy to assist you - if you won't find the answer to these smaller questions before.
If you can put it out in pseudocode, it would be easier. There's all kinds of text-manipulating stuff in unix. The means to employ depend on how big are your texts. I believe they are not so big, or you would have used some compiled language.
For example the easy but costly gawk way to count frequences:
awk -F "" '{for(i=1;i<=NF;i++) freq[$i]++;}END{for(i in freq) printf("%c %d\n", i, freq[i]);}'
As for transliterating, there is tr utility. You can forge and then pass to it the actual strings in each case (that stands true for Caesar-like ciphers).
grep -o . inputfile | sort | uniq -c | sort -rn
Example:
$ echo 'aAAbbbBBBB123AB' | grep -o . | sort | uniq -c | sort -rn
5 B
3 b
3 A
1 a
1 3
1 2
1 1