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Full Discussion: reverse tokens with sed
Top Forums Shell Programming and Scripting reverse tokens with sed Post 302169636 by markc on Thursday 21st of February 2008 09:33:58 PM
Old 02-21-2008
reverse tokens with sed

I currently use this bash for loop below to reverse a set of tokens, example "abc def ghi" to "ghi def abc" but in looking at various sed one liner postings I notice two methods to reverse lines of text from a file (emulating tac) and reversing letters in a string (emulating rev) so I've spent some time on how to reverse string tokens using sed, but I'm getting nowhere fast. Any suggestions welcome on how to use sed to reverse a series of string tokens as per this for loop example.

Code:
TOKENS="abc def ghi"; for i in $TOKENS; do STR="$i $STR"; done; echo $STR
ghi def abc

And these are the 2 sed one liners...

Code:
# reverse order of lines (emulates "tac")
sed '1!G;h;$!d'               # method 1
sed -n '1!G;h;$p'             # method 2

# reverse each character on the line (emulates "rev")
sed '/\n/!G;s/\(.\)\(.*\n\)/&\2\1/;//D;s/.//'


Last edited by markc; 02-21-2008 at 11:01 PM..
 

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Char(3pm)						User Contributed Perl Documentation						 Char(3pm)

NAME
PDL::Char -- PDL subclass which allows reading and writing of fixed-length character strings as byte PDLs SYNOPSIS
use PDL; use PDL::Char; my $pchar = PDL::Char->new( [['abc', 'def', 'ghi'],['jkl', 'mno', 'pqr']] ); $pchar->setstr(1,0,'foo'); print $pchar; # 'string' bound to "", perl stringify function # Prints: # [ # ['abc' 'foo' 'ghi'] # ['jkl' 'mno' 'pqr'] # ] print $pchar->atstr(2,0); # Prints: # ghi DESCRIPTION
This subclass of PDL allows one to manipulate PDLs of 'byte' type as if they were made of fixed length strings, not just numbers. This type of behavior is useful when you want to work with charactar grids. The indexing is done on a string level and not a character level for the 'setstr' and 'atstr' commands. This module is in particular useful for writing NetCDF files that include character data using the PDL::NetCDF module. FUNCTIONS
new Function to create a byte PDL from a string, list of strings, list of list of strings, etc. # create a new PDL::Char from a perl array of strings $strpdl = PDL::Char->new( ['abc', 'def', 'ghij'] ); # Convert a PDL of type 'byte' to a PDL::Char $strpdl1 = PDL::Char->new (sequence (byte, 4, 5)+99); $pdlchar3d = PDL::Char->new([['abc','def','ghi'],['jkl', 'mno', 'pqr']]); string Function to print a character PDL (created by 'char') in a pretty format. $char = PDL::Char->new( [['abc', 'def', 'ghi'], ['jkl', 'mno', 'pqr']] ); print $char; # 'string' bound to "", perl stringify function # Prints: # [ # ['abc' 'def' 'ghi'] # ['jkl' 'mno' 'pqr'] # ] # 'string' is overloaded to the "" operator, so: # print $char; # should have the same effect. setstr Function to set one string value in a character PDL. The input position is the position of the string, not a character in the string. The first dimension is assumed to be the length of the string. The input string will be null-padded if the string is shorter than the first dimension of the PDL. It will be truncated if it is longer. $char = PDL::Char->new( [['abc', 'def', 'ghi'], ['jkl', 'mno', 'pqr']] ); $char->setstr(0,1, 'foobar'); print $char; # 'string' bound to "", perl stringify function # Prints: # [ # ['abc' 'def' 'ghi'] # ['foo' 'mno' 'pqr'] # ] $char->setstr(2,1, 'f'); print $char; # 'string' bound to "", perl stringify function # Prints: # [ # ['abc' 'def' 'ghi'] # ['foo' 'mno' 'f'] -> note that this 'f' is stored "f" # ] atstr Function to fetch one string value from a PDL::Char type PDL, given a position within the PDL. The input position of the string, not a character in the string. The length of the input string is the implied first dimension. $char = PDL::Char->new( [['abc', 'def', 'ghi'], ['jkl', 'mno', 'pqr']] ); print $char->atstr(0,1); # Prints: # jkl perl v5.14.2 2011-03-30 Char(3pm)
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