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Top Forums UNIX for Dummies Questions & Answers String substitutions in ASCII files - Post 23972 by Perderabo on Wednesday 3rd of July 2002 09:16:51 AM
Old 07-03-2002
The exact best approach would depend on the details of your particular system. It always amazes me when folks ask questions without revealing what version of unix, what computer, etc. Well, I'll this a shot anyway.

The fastest way to do anything is to write a carefully designed assembly language program that will fully exploit the features available on your system. Following close behind would be writing the program in C.

As far as scripts go, the fastest way to to perform the two tranformations that you mentioned is this:
Code:
#! /usr/bin/sed -f
s/London/X1/g
s/Frankfurt/X2/g

You might call it "scramble" and run it like this:
./scramble < inputfile > outputfile

But you want to do 400 substitutions. sed will have some limit on the number of commands that it can handle. It is not likely that you can get all 400 in one script. You can probably get 100, but the exact limit depends on your version of unix. You could have 4 of these, like this:
./scramble1 < input | ./scramble2 | ./scramble3 | ./scramble4 > output
If your computer has at least 4 cpu's this might still be unbeatable by any other scripted solution.

The latest version of ksh, ksh93, has much of sed built-in. A carefully written ksh93 script that relies only on built-ins could probably beat the pipeline of sed scripts. But most folks only have ksh88 available.

Try the sed solution and see where that leaves you.

Last edited by Perderabo; 07-03-2002 at 10:22 AM..
 

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strings(1)							   User Commands							strings(1)

NAME
strings - find printable strings in an object or binary file SYNOPSIS
strings [-a | -] [-t format | -o] [-n number | -number] [file...] DESCRIPTION
The strings utility looks for ASCII strings in a binary file. A string is any sequence of 4 or more printing characters ending with a new- line or a null character. strings is useful for identifying random object files and many other things. OPTIONS
The following options are supported: -a | - Look everywhere in the file for strings. If this flag is omitted, strings only looks in the initialized data space of object files. -n number | -number Use a number as the minimum string length rather than the default, which is 4. -o Equivalent to -t d option. -t format Write each string preceded by its byte offset from the start of the file. The format is dependent on the single character used as the format option-argument: d The offset will be written in decimal. o The offset will be written in octal. x The offset will be written in hexadecimal. OPERANDS
The following operand is supported: file A path name of a regular file to be used as input. If no file operand is specified, the strings utility will read from the stan- dard input. ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of strings: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH. EXIT STATUS
The following exit values are returned: 0 Successful completion. >0 An error occurred. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWtoo | +-----------------------------+-----------------------------+ |CSI |Enabled | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
od(1), attributes(5), environ(5), standards(5) NOTES
The algorithm for identifying strings is extremely primitive. For backwards compatibility, the options -a and - are interchangeable. SunOS 5.10 20 Dec 1996 strings(1)
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