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Full Discussion: sed internal working
Top Forums Shell Programming and Scripting sed internal working Post 302494121 by Perderabo on Saturday 5th of February 2011 09:49:27 AM
Old 02-05-2011
The most important factor to writing fast shell scripts is to minimize the number of external programs invoked. It is a big deal to create a new process, go find the file containing sed or awk, open it, read it in, transfer control it, wait for it to exit, reclaim the process' resources and deliver the return code to the shell. When I need to manipulate a string I would rather code a dozen internal shell operations that invoke a single copy of sed. This is especially true of string manipulation in a loop.

Once a decision hs been made to invoke an external program, some are faster than others, but this is a relatively minor consideration. sed can tackle fewer jobs than awk. It's a much smaller program than awk. awk always tries to crack a line into fields whether or not this is useful. So sed can outperform awk on the tasks that sed can easily do. tr is smaller still and can outperform sed on the even smaller setset of tasks that tr can handle. But I rarely spend a lot of time worrying about stuff like this. They are all external programs. I try to avoid as many as possible.

Of all of the shell scripts I have posted on this site, the most frequently used is datecalc. And datecalc invokes no external programs at all.
datecalc
 

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PYP(1)							      General Commands Manual							    PYP(1)

NAME
pyp - The Pyed Piper: A Modern Python Alternative to awk, sed and Other Unix Text Manipulation Utilities SYNOPSIS
pyp [options] files ... DESCRIPTION
pyp, the Pyed Piper, is a command line tool for text manipulation. It is similar to awk and sed in functionality, but its subcommands are Python based, and thus more familiar to many programmers. It can operate both on a per-line base and on the complete input stream. Different features can be pipelined in a single command by using the pipe character familiar from shell commands. pyp backs up its input for reruns with modified commands, and can save commands as macros. On the downside, the rerun feature makes it unsuitable for continuous pipe operation. OPTIONS
These programs follow the usual GNU command line syntax, with long options starting with two dashes (`-'). A summary of options is included below. For a complete description, use --manual. -h, --help Show this help message and exit. -m, --manual Prints out extended help. -l, --macro_list Lists all available macros. -s MACRO_SAVE_NAME, --macro_save=MACRO_SAVE_NAME Saves current command as macro. use "#" for adding comments EXAMPLE: pyp -s "great_macro # prints first letter" "p[1]". -f MACRO_FIND_NAME, --macro_find=MACRO_FIND_NAME Searches for macros with keyword or user name. -d MACRO_DELETE_NAME, --macro_delete=MACRO_DELETE_NAME Deletes specified public macro. -g, --macro_group Specify group macros for save and delete; default is user. -t TEXT_FILE, --text_file=TEXT_FILE Specify text file to load. For advanced users, you should typically cat a file into pyp. -x, --execute Execute all commands. -c, --turn_off_color Prints raw, uncolored output. -u, --unmodified_config Prints out generic PypCustom.py config file. -b BLANK_INPUTS, --blank_inputs=BLANK_INPUTS Generate this number of blank input lines; useful for generating numbered lists with variable 'n'. -n, --no_input Use with command that generates output with no input; same as --dummy_input 1. -k, --keep_false Print blank lines for lines that test as False. default is to filter out False lines from the output. -r, --rerun Rerun based on automatically cached data from the last run. Use this after executing "pyp", pasting input into the shell, and hitting CTRL-D. SEE ALSO
awk(1), grep(1), sed(1). AUTHOR
pyp was written by Toby Rosen <tobyrosen@gmail.com>. This manual page was written by Khalid El Fathi <khalid@elfathi.fr>, for the Debian project (and may be used by others). March 19, 2012 PYP(1)
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