See:

• http://www.pement.org/awk/awk1line.txt
• http://sed.sourceforge.net/sed1line.txt

One-liner is preferred to run from

python -c 'ONE_LINER'

• double space a file

import sys; print "\n".join(line for line in sys.stdin)

• double space a file which already has blank lines in it. Output file should contain no more than one blank line between lines of text.

import sys; print "\n".join(line for line in sys.stdin if not len(line) == 0 )

• triple space a file

import sys; print "\n\n".join(line for line in sys.stdin)

• precede each line by its line number FOR THAT FILE (left alignment). Using a tab (\t) instead of space will preserve margins.

import sys; print "".join("%d\t%s"%(n + 1, line) for (n, line) in enumerate(sys.stdin))

• precede each line by its line number FOR ALL FILES TOGETHER, with tab.

import sys,glob; map(lambda file: sys.stdout.write("".join("%d\t%s"%(n + 1, line) for(n, line) in enumerate(open(file)))), glob.glob("*"));

• number each line of a file (number on left, right-aligned) Double the percent signs if typing from the DOS command prompt.

import sys; print "".join("%5d %s"%(n + 1, line) for (n, line) in enumerate(sys.stdin))

• number each line of file, but only print numbers if line is not blank. Remember caveats about Unix treatment of \r (mentioned above)

import sys; print "".join("%5d %s"%(n + 1, line) for (n, line) in enumerate(sys.stdin) if len(line)>0)

• count lines (emulates “wc -l”)

import sys; print sum(1 for line in sys.stdin)

To be continued…