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wc command

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The wc command stands for "word count". It reads one or more input files and, by default, writes the number of newline characters, words and bytes contained in each input file to the standard output. Most often used as the last stage of pipes like ps -e | wc -l

If more than one input file is specified, a line of cumulative count(s) for each of specified files as well as is total count for all files is printed.

    3 rarme.bat
   11 robots.txt
  334 safary.shtml
 2993 strange_files.txt
    1 today.lst
   18 topbooks.htm
   37 topupdates.htm
   38 topvisited.htm
   15 update.bat
18791 total

When an option is specified, wc only reports the information requested by that option. Option -w counts words. Historically, the wc defines a word as a ``maximal string of characters delimited by <space>, <tab> or <newline> characters''. Such a definition creates problem with non-printable characters. Most modern implementations defines a ``word'' in terms of the isspace(3) function, as required by IEEE Std1003.2-1992 (``POSIX.2'').

The default behavior presuppose options -clw having been specified.


The following options are supported:
  1. -c Counts bytes.
  2. -C Same as -m.
  3. -l Counts lines.
  4. -m Counts characters.
  5. -w Counts words delimited by white space characters -- Extended Unix Code (EUC) characters from any code set defined by iswspace().

If no option is specified, the default is -lwc (counts lines, words, and bytes.). The -c and -m options are mutually exclusive.


who | wc -l

counts the number of users logged

ps -e | wc -l

counts the number of processes

ls -l | grep ^d | wc -l # finds the number of subdirectories in the current directory.

wc -l /etc/passwd

tells you the number of lines (accounts) in the /etc/passwd file.

wc -w readme.txt

counts the number of words in the file named readme.txt

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Old News ;-)

[Feb 10, 2007] Useless Use of wc Award

Useless Use of wc -l

This is my personal favorite. There is actually a whole class of "Useless Use of (something) | grep (something) | (something)" problems but this one usually manifests itself in scripts riddled by useless backticks and pretzel logic.

Anything that looks like

something | grep '..*' | wc -l
can usually be rewritten like something along the lines of
something | grep -c .   # Notice that . is better than '..*'
or even (if all we want to do is check whether something produced any non-empty output lines)
something | grep . >/dev/null && ...
(or grep -q if your grep has that).

If something is reasonably coded, it might even already be setting its exit code to tell you whether it succeeded in doing what you asked it to do; in that case, all you have to check is the exit code:

something && ...

I used to have a really wretched example of clueless code (which I had written up completely on my own, to protect the innocent) which I've moved to a separate page and annotated a little bit. It expands on the above and also has a bit about useless use of backticks (q.v.)


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