www.ptug.org/sed/one_liners.html
Using a tab (see # note on '\t' at end of file) instead of space will preserve margins. In method 1, # spaces at the beginning of the line are significant, and trailing # spaces are appended at the end of the line. In method 2, spaces at # the beginning of the line are discarded in centering the line, and # no trailing spaces appear at the end of lines. The 'echo' # command may need an -e switch if you use Unix System V or bash shell. Files passed to # sed must be passed in the proper order. TXT file # (under DOS: the "dir /b" switch returns bare filenames in all caps). After all the commands have been applied to the first input line, that line is output and a second input line is taken for processing, and the cycle repeats. One or more filenames can be appended to the command line if the input does not come from stdin. Thus: cat filename | sed '10q' # uses piped input sed '10q' filename # same effect, avoids a useless "cat" sed '10q' filename > newfile # redirects output to disk For additional syntax instructions, including the way to apply editing commands from a disk file instead of the command line, consult "sed & awk, 2nd Edition," by Dale Dougherty and Arnold Robbins (O'Reilly, 1997; The manual ("man") pages on Unix systems may be helpful (try "man sed", "man regexp", or the subsection on regular expressions in "man ed"), but man pages are notoriously difficult. They are not written to teach sed use or regexps to first-time users, but as a reference text for those already acquainted with these tools. USE OF '\t' IN SED SCRIPTS: For clarity in documentation, we have used the expression '\t' to indicate a tab character (0x09) in the scripts. However, most versions of sed do not recognize the '\t' abbreviation, so when typing these scripts from the command line, you should press the TAB key instead. VERSIONS OF SED: Versions of sed do differ, and some slight syntax variation is to be expected. In particular, most do not support the use of labels (:name) or branch instructions (b,t) within editing commands, except at the end of those commands. We have used the syntax which will be portable to most users of sed, even though the popular GNU versions of sed allow a more succinct syntax. Thus: sed 's/foo/bar/g' filename # standard replace command sed '/foo/ s/foo/bar/g' filename # executes more quickly sed '/foo/ s//bar/g' filename # shorthand sed syntax On line selection or deletion in which you only need to output lines from the first part of the file, a "quit" command in the script will drastically reduce processing time for large files. Indicate the version of sed you used, the operating system it was compiled for, and the nature of the problem.
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