Softpanorama (slightly skeptical) Open Source Software Educational Society

May the source be with you, but remember the KISS principle ;-)

Unix wc command

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
  124 truncate2.pl
   15 update.bat
    1 xcopy_sp.sh
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.

Options

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.

Examples

who | wc -l

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

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.)

Reference

Solaris 9 Reference Manual Collection

wc- display a count of lines, words and characters in a file

 

wc [-c| -m| -C] [-lw] [file...]


The wc utility 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.

The utility also writes a total count for all named files, if more than one input file is specified.

wc considers a word to be a non-zero-length string of characters delimited by white space (for example, SPACE, TAB ). See iswspace(3C) or isspace(3C).

OPTIONS

The following options are supported:

-c

Count bytes.

-m

Count characters.

-C

Same as -m.

-l

Count lines.

-w

Count words delimited by white space characters or new line characters. Delimiting characters are Extended Unix Code (EUC) characters from any code set defined by iswspace().

If no option is specified the default is -lwc (count lines, words, and bytes.)

OPERANDS

The following operand is supported:

file

A path name of an input file. If no file operands are specified, the standard input will be used.

USAGE

See largefile(5) for the description of the behavior of wc when encountering files greater than or equal to 2 Gbyte ( 2³¹ bytes).

ENVIRONMENT VARIABLES

See environ(5) for descriptions of the following environment variables that affect the execution of wc: LC_CTYPE, LC_MESSAGES, and NLSPATH.

EXIT STATUS

The following exit values are returned:

0

Successful completion.

>0

An error occurred.

Last modified: September 15, 2008