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ksh check for non printable characters in a string


 
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# 1  
ksh check for non printable characters in a string

Hi All,

I am trying to find non-printable characters in a string. The sting could have alphanumeric, puntuations and characters like (*&%$#.') but not non-printable (or that is what I think they are called) which are introduced when you copy any text from DOS to unix box.

Input string1:
Code:
 TEXT="This is a sample text with supposedly non-printable character^Y."

Input string2:
Code:
TEXT="This is a sample text with supposedly non-printable character"

I've got a code from the website for bash but still this is not working.

Code:
if ! [[ "$TEXT" =~ ^[a-zA-Z0-9]+$ ]];then echo "invalid"; fi

Note: I've removed the dot also "." from "Input string2" just to check if the command works or not.

This prints "invalid" in both the cases?! Also is there any equivalent command that works in KSH? Please suggest.

-dips

Last edited by rbatte1; 02-10-2015 at 06:12 AM.. Reason: Tightened CODE tags
# 2  
Your pattern is treating <space> as a non-printable character and, since it is present in both strings, you are getting invalid for both.

For a more portable test that should work with any POSIX conforming shell, try:
Code:
if [ "${TEXT#*[![:print:]]}" = "$TEXT" ];then echo 'no non-printables found';else echo 'non-printable found';fi

# 3  
Hi Don,

Thanks for telling me that <space> is being treated like non-printable character. But I want this seach to look for all NON UTF-8 characters actually, I don't have any inkling on how to check those?

The XML file of the application takes only UTF-8 characters and anything other than this will not let the jobs run through this application. Hence is there any way to check for UTF-8 characters? Can you please suggest?

For e.g.
Code:
TEXT="This is a sample text with supposedly non-printable character^Y."

The highlighted character shown in the file is what I've in my application which when seen in unix appears to be ^Y. How to identify such characters?

-dips
ksh check for non printable characters in a string-special_charpng
# 4  
If what you show as ^Y represents <CTRL> Y (0x19, "EM"), it is member of the ASCII char set which in turn is a subset of UTF-8. Although there exist byte sequences that are not valid UTF-8 characters, they should not show up in texts or HTML files, unless created by a failed transmission or conversion.
Please show us a hexdump (od -ctx1 file) of your problematic file.
# 5  
This works in ksh93 or bash3:
Code:
if [[ $TEXT =~ [^[:print:]] ]] ; then echo invalid; fi

# 6  
Hi,

I'll be not able to convert it to hex file.

But in a simplest manner, can I check for only alphanumeric characters plus few punctuations which I know will get passed?

Code:
if [ "${TEXT#*[![:alnum:]][.,;:'"/\()-_+=~@&*]}" = "$TEXT" ];then echo 'no non-printables found';else echo 'non-printable found';fi

This is clearly not working. Can you please help me?
-dips
# 7  
Quote:
Originally Posted by dips_ag
Hi,

I'll be not able to convert it to hex file.

But in a simplest manner, can I check for only alphanumeric characters plus few punctuations which I know will get passed?

Code:
if [ "${TEXT#*[![:alnum:]][.,;:'"/\()-_+=~@&*]}" = "$TEXT" ];then echo 'no non-printables found';else echo 'non-printable found';fi

This is clearly not working. Can you please help me?
-dips
You have the syntax off a little bit, but that is close (and I assume you don't want <space> to cause a "non-printable found" either). Try:
Code:
if [ "${TEXT#*[![:alnum:] .,;:'"/\()_+=~@&*-]}" = "$TEXT" ];then echo 'no non-printables found';else echo 'non-printable found';fi

Note that a space was added, one pair of square brackets was removed, and the minus sign was moved to the end of the non-matching bracket expression element list.

And, yes you can convert your string to hex:
Code:
printf '%s' "$TEXT" | od -t co1x1

will display your string as characters, octal bytes, and hex bytes. (If your version of od doesn't have a -t option, just use:
Code:
printf '%s' "$TEXT" | od -cb

to get character and octal byte output.)

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