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Top Forums Shell Programming and Scripting parsing a string in a shell script Post 54201 by zazzybob on Thursday 5th of August 2004 08:13:10 AM
Old 08-05-2004
Sure
Code:
substr( s, i, n )

Where:

s is the string you want to perform the substr operation on
i is the first character that you want to extract
n is the last character you want to match

So if you said substr( "hello", 2, 4 ) it would match the second, third and fourth character and return ell.

Let me explain the code I gave

Code:
$ echo "welcome" | awk '{ print substr( $0, 0, 4 ) }'

In the above example, the first argument to substr is $0 (which in this case is the text piped to it - "$0" is the entire record). The second argument is 0 (I could also have used 1) because I want to match from the start of the string. I want to grab the first four characters, so the third argument is 4.

Code:
$ echo "welcome" | awk '{ print substr( $0, length($0) - 3, length($0) ) }'

The above code also makes use length(string) command to return the number of characters in the string.
So here, I'm saying "return the substring from the first character (which is the length of the string minus 3), up until the very end of the string".

To clarify this:
Code:
$ echo "welcome" | awk '{ print (length($0) - 3), length($0) }'
4 7

So in our substr, we grab from character 4 to character 7 inclusive, which are chars 4,5,6,7 - the last 4 chars.

Last edited by rbatte1; 01-26-2017 at 07:22 AM..
 

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tapset::string(3stap)													     tapset::string(3stap)

NAME
tapset::string - systemtap string tapset DESCRIPTION
strlen Returns the length of a string See function::strlen(3stap) for details. substr Returns a substring See function::substr(3stap) for details. stringat Returns the char at a given position in the string See function::stringat(3stap) for details. isinstr Returns whether a string is a substring of another string See function::isinstr(3stap) for details. text_str Escape any non-printable chars in a string See function::text_str(3stap) for details. text_strn Escape any non-printable chars in a string See function::text_strn(3stap) for details. - strtol Convert a string to a long See function::-strtol(3stap) for details. isdigit Checks for a digit See function::isdigit(3stap) for details. SEE ALSO
function::strlen(3stap), function::substr(3stap), function::stringat(3stap), function::isinstr(3stap), function::text_str(3stap), function::text_strn(3stap), function::-(3stap), function::strtol(3stap), function::isdigit(3stap), stap(1), stapprobes(3stap) IBM
--- tapset::string(3stap)
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